Remove Vim runtime path set as an environmental path.

Remove the Vim runtime path we've previously set as an environmental
variable. It's no longer necessary now that we install Vim via Linuxbrew,
which installs Vim's runtime files.
Remove rbenv autocompletion setup from `.profile` file.
Add color to man pages when used with less.
Display Git branch information as part of the prompt.
Refactor bash configuration content.

Refactor bash configuration content to take advantage of Linxubrew, and
move bash functions into a separate file.