Updated README and added Markdown support

Added a paragraph to the README about supporting other file types
and added support for Markdown files.  Added some words to the
dictionary so that the README.md passes the spell checker.

Author: dave3d

README.md

@@ -32,3 +32,10 @@ If a word is not found in the dictionaries, we try two additional checks.
 ...camel-case words such as 'GetArrayFromImage', which would get split into
 ...'Get', 'Array', 'From', and 'Image'.  Camel-case words are very commonly
 ...used for code elements.
+
+The script can also process other file types.  With the **'--suffix'**
+option, the following file types are available: Python (.py), C/C++
+(.c/.cxx), Text (.txt), reStructuredText(.rst), Markdown (.md), Ruby (.ruby),
+and Java (.java).  Note that reStructuredText files are treated as standard
+text.  Consequentially, all markup keywords that are not actual words will
+need to be added to the additional/exception dictionary.

additional_dictionary.txt

@@ -923,6 +923,7 @@ clientdata
 closedness
 codebook
 codebooks
+codespell
 codeword
 codewords
 codimension
@@ -1165,6 +1166,7 @@ getsizeof
 getter
 ggplot
 gimble
+github
 globals
 gmail
 goodbit
@@ -1560,6 +1562,7 @@ public
 putback
 pv
 py
+pyenchant
 pyplot
 qe
 ql
@@ -1722,6 +1725,7 @@ superpixel
 supersampling
 superset
 svd
+svg
 swapaxes
 sweepline
 switch
@@ -1885,6 +1889,7 @@ xyz
 xz
 ymax
 ymin
+yml
 yn
 yy
 yyy