Add miscellaneous projections descriptions (#762)

* Add description on misc_eckertIV.py

* Add description on misc_eckertVI.py

* Add description on misc_hammer.py

* Add description on misc_mollweide.py

* Add description on misc_robinson.py

* Add description on misc_sinusoidal.py

* Add description on misc_van_der_grinten.py

* Add description on misc_winkel_tripel.py

Author: willschlitzer

examples/projections/misc/misc_eckertIV.py

@@ -2,6 +2,11 @@
 Eckert IV
 =========
 
+The Eckert IV projection, presented by the German cartographer Max
+Eckert-Greiffendorff in 1906, is a pseudo-cylindrical equal-area projection. Central
+meridian and all parallels are straight lines; other meridians are equally spaced
+elliptical arcs. The scale is true along latitude 40°30’.
+
 ``Kf[central meridian]/width``: Give the optional central meridian (default is the
 center of the region) and the map width.
 """

examples/projections/misc/misc_eckertVI.py

@@ -2,6 +2,11 @@
 Eckert VI
 =========
 
+The Eckert VI projections, presented by the German cartographer
+Max Eckert-Greiffendorff in 1906, is a pseudo-cylindrical equal-area projection.
+Central meridian and all parallels are straight lines; other meridians are equally
+spaced sinusoids. The scale is true along latitude 49°16’.
+
 ``Ks[central meridian]/width``: Give the optional central meridian (default is the
 center of the region) and the map width.
 """

examples/projections/misc/misc_hammer.py

@@ -2,6 +2,11 @@
 Hammer
 ======
 
+The equal-area Hammer projection, first presented by the German mathematician
+Ernst von Hammer in 1892, is also known as Hammer-Aitoff (the Aitoff projection looks
+similar, but is not equal-area). The border is an ellipse, equator and central
+meridian are straight lines, while other parallels and meridians are complex curves.
+
 ``H[central meridian]/width``: Give the optional central meridian (default is the center
  of the region) and the map width.
 """

examples/projections/misc/misc_mollweide.py

@@ -2,6 +2,13 @@
 Mollweide
 =========
 
+This pseudo-cylindrical, equal-area projection was developed by the German
+mathematician and astronomer Karl Brandan Mollweide in 1805. Parallels are unequally
+spaced straight lines with the meridians being equally spaced elliptical arcs. The
+scale is only true along latitudes 40°44’ north and south. The projection is used
+mainly for global maps showing data distributions. It is occasionally referenced under
+the name homalographic projection.
+
 ``W[central meridian]/width``: Give the optional central meridian (default is the center
  of the region) and the map width.
 """

examples/projections/misc/misc_robinson.py

@@ -2,6 +2,14 @@
 Robinson
 ========
 
+The Robinson projection, presented by the American geographer and cartographer
+Arthur H. Robinson in 1963, is a modified cylindrical projection that is neither
+conformal nor equal-area. Central meridian and all parallels are straight lines; other
+meridians are curved. It uses lookup tables rather than analytic expressions to make
+the world map “look” right 22. The scale is true along latitudes 38. The projection was
+originally developed for use by Rand McNally and is currently used by the
+National Geographic Society.
+
 ``N[central meridian]/width``: Give the optional central meridian (default is the center
  of the region) and the map width.
 """

examples/projections/misc/misc_sinusoidal.py

@@ -2,6 +2,12 @@
 Sinusoidal
 ==========
 
+The sinusoidal projection is one of the oldest known projections, is equal-area, and
+has been used since the mid-16th century. It has also been called the
+“Equal-area Mercator” projection. The central meridian is a straight line; all other
+meridians are sinusoidal curves. Parallels are all equally spaced straight lines, with
+scale being true along all parallels (and central meridian).
+
 ``I[central meridian]/width``: Give the optional central meridian (default is the center
  of the region) and the map width.
 """

examples/projections/misc/misc_van_der_grinten.py

@@ -2,6 +2,11 @@
 Van der Grinten
 ===============
 
+The Van der Grinten projection, presented by Alphons J. van der Grinten in 1904, is
+neither equal-area nor conformal. Central meridian and Equator are straight lines;
+other meridians are arcs of circles. The scale is true along the Equator only. Its
+main use is to show the entire world enclosed in a circle.
+
 ``V[central meridian]/width``: Give the optional central meridian (default is the center
  of the region) and the map width.
 """

examples/projections/misc/misc_winkel_tripel.py

@@ -2,6 +2,20 @@
 Winkel Tripel
 =============
 
+In 1921, the German mathematician Oswald Winkel a projection that was to strike a
+compromise between the properties of three elements (area, angle and distance). The
+German word “tripel” refers to this junction of where each of these elements are least
+distorted when plotting global maps. The projection was popularized when Bartholomew
+and Son started to use it in its world-renowned “The Times Atlas of the World” in the
+mid-20th century. In 1998, the National Geographic Society made the Winkel Tripel as
+its map projection of choice for global maps.
+
+Naturally, this projection is neither conformal, nor equal-area. Central meridian and
+equator are straight lines; other parallels and meridians are curved. The projection is
+obtained by averaging the coordinates of the Equidistant Cylindrical and Aitoff
+(not Hammer-Aitoff) projections. The poles map into straight lines 0.4 times the
+length of equator.
+
 ``R[central meridian]/width``: Give the optional central meridian (default is the center
  of the region) and the map width.
 """