Bash: Change MacVim to Macports MacVim

I had to do switch to Macports in order to use Vim's YouCompleteMe
plugin. YouCompleteMe kept failing because of conflict between the
Python version it was compiled against versus MacVim python version.

I resorted to Macports MacVim to make it work.
Vim: Use YouCompleteMe for code completion
Vim: Swap snipmate with ultisnips plugin

Ultisnips works with YouCompleteMe and is more actively maintained than
snipmate.
Vim: Configure ultisnips and add vim-snippets project
Vim: Add snippet for Pelican new article meta data in Markdown
Vim: Add Narrow Region and Git wrapper plugin
Vim: Add syntax highlight rules for NERDTree window
Vim: Configure NERDTree
Vim: Do not launch NERDTree in git commit and rebase editor
Vim: Add repeat, tagbar, tcomment and session plugins
Vim: Add sessions directory to gitignore
Vim: Configure Voom to open on right hand side
Vim: Remove unnecessary comments and white spaces
Vim: Replace Powerline with Airline

Powerline's CTRLP plug was broken. There are many open pull requests at
the official repo that goes back to couple of months. Airline is much
more stable.
Vim: Configure CtrlP to ignore files to improve speed