Use a serif font in GVim.

Serif fonts look good on my new Macbook's retina display.
Add ~/.cabal/bin to PATH.

Cabal is the Haskell Platform's package manager.
I just installed it, primarily to use it to install Pandoc.
Add tmux-irb to launch irb in a new tmux panel.
Add cg function; simplify Bash prompt.

The cg function cds to the root of the current Git repo.

The simplified prompt avoids confusing Bash.  Variable-length prompts
seem to mess up C-u line clearing, as well as line wrapping.
Ignore hidden files (.*) for tab completion.
Add bindings to Vim for Ruby files.