Only include twitter buttons if present in project.

Merge pull request #132 from ehmatthes/small_fixes

Changed heading styles to bootstrap, not nbconvert.

Merge pull request #131 from ehmatthes/programming_environment

Updated links to osx programming environment.

Finished osx programming environment.

Almost finished osx programming environment.

Minor formatting fix to Windows programming environment.

Merge pull request #130 from ehmatthes/programming_environment

Updated Windows programming environment.

Minor fixes to Linux programming environment.

Merge pull request #129 from ehmatthes/programming_environment

Updated linux programming environment notes.

Updated overall programming environment notebook.

Merge pull request #127 from ehmatthes/small_fixes