Fix spelling mistakes, add Go Report Card badge

Author: bluekeyes

README.md

@@ -1,6 +1,6 @@
 # go-gitdiff
 
-[![GoDoc](https://godoc.org/github.com/bluekeyes/go-gitdiff/gitdiff?status.svg)](http://godoc.org/github.com/bluekeyes/go-gitdiff/gitdiff)
+[![GoDoc](https://godoc.org/github.com/bluekeyes/go-gitdiff/gitdiff?status.svg)](http://godoc.org/github.com/bluekeyes/go-gitdiff/gitdiff) [![Go Report Card](https://goreportcard.com/badge/github.com/bluekeyes/go-gitdiff)](https://goreportcard.com/report/github.com/bluekeyes/go-gitdiff)
 
 A Go library for parsing and applying patches generated by `git diff`, `git
 show`, and `git format-patch`. It can also parse and apply unified diffs

gitdiff/file_header.go

@@ -302,7 +302,7 @@ func parseMode(s string) (os.FileMode, error) {
 
 // parseName extracts a file name from the start of a string and returns the
 // name and the index of the first character after the name. If the name is
-// unquoted and term is non-negative, parsing stops at the first occurance of
+// unquoted and term is non-negative, parsing stops at the first occurrence of
 // term. Otherwise parsing of unquoted names stops at the first space or tab.
 //
 // If the name is exactly "/dev/null", no further processing occurs. Otherwise,

gitdiff/file_header_test.go

@@ -368,7 +368,7 @@ func TestParseName(t *testing.T) {
 			}
 
 			if output != test.Output {
-				t.Errorf("incorect output: expected %q, actual: %q", test.Output, output)
+				t.Errorf("incorrect output: expected %q, actual: %q", test.Output, output)
 			}
 			if n != test.N {
 				t.Errorf("incorrect next position: expected %d, actual %d", test.N, n)

gitdiff/gitdiff.go

@@ -56,7 +56,7 @@ type TextFragment struct {
 	Lines []Line
 }
 
-// Header returns the cannonical header of this fragment.
+// Header returns the canonical header of this fragment.
 func (f *TextFragment) Header() string {
 	return fmt.Sprintf("@@ -%d,%d +%d,%d @@ %s", f.OldPosition, f.OldLines, f.NewPosition, f.NewLines, f.Comment)
 }