Correct spelling of 'aforementioned'.
Nitpicky rewordings and grammar fixes.
Add line breaks for conformance with the Style Guide.
GtK --> GTK
'many' --> 'much'
PEP and Python are capitalized.
'async' --> 'asynchronous'
Code block type is 'console', not 'bash'.
Added note about OSX-GCC-Installer and Xcode conflict.
Merge pull request #284 from kuyan/master

Grammar, capitalization fixes