add clear sky documentation page (#209)

* add clearsky doc page

* edits

* more edits

* more edits

* ineichen examples

* more edits

* use very long single line input for problematic plots

* try using matplotlib 2.0.0 pre release

* try 3.5

* remove ipython version

* remove all versions

* add mpl import to conf.py

* add matplotlib use agg to conf

* add use agg to clearsky

* add some prints

* add oks

* ipython_mplbackend = None

* change a few imports

* ipython_mplbackend = Agg

* add print to conf

* remove some ;

* add verbatims

* get rid of :: pythons

* prev commit compiles! now remove verbatims...

* start adding ipython prompts

* more ipython prompts

* add blank lines

* roll back env changes. more prompts

* lots more ipython prompts

* fix an ipython line continuation problem

* code-block the turbidity section

* stop after scipy.io call

* make first turbidity map

* no images, but make turbidity line plots

* make the image but dont save it

* everything but imshow

* make image but without data

* make image but without data

* remove slice

* add code block

* dont print linke_turbidity_table

* before mat

* mat without getitem

* mat with getitem but not divide

* add divide by 20.

* add astype(np.float64)

* only convert to float, no divide

* convert to int

* add slice

* add nomkl

* scipy 0.16.0

* scipy 0.16.0 and nomkl

* try a different casting approach

* go back to a working state

* does a simple uint8 to float crash?

* does a simple uint8 to float crash?

* plot in native file units

* fix typo

* minor edits

Author: wholmgren