Add Python excludes to .gitignore.
Add C++ excludes to .gitignore.
Add C excludes to .gitignore.
Add Haskell excludes to .gitignore.
Remove comments from .gitignore.

Preparing for removing duplicates.
Sort entries in .gitignore. Preparing to remove duplicates and useless
excludes.
Cleanup .gitignore.
Add swap files to .gitignore.