Teach Ack to search Markdown files
Remove obsolete inputrc

https://github.com/jasonrudolph/keyboard/commit/959ff6908ff negates the
need for this inputrc file.
Display file sizes in mortal-friendly format
Instruct Git to ignore tags files

Ignore the ctags files created by https://github.com/SublimeText/CTags.
Remove git user initials from bash prompt
Clean up whitespace
Remove unused PS1 setting

This setting gets overridden in bash/gitprompt.
Ditch xterm-color setting

This setting (or this setting in combination with my other current
settings) causes weird issues with bash history. The issues are similar
to the problems described in these posts, but those solutions didn't
seem to do the trick for me:

- http://unix.stackexchange.com/questions/31642/bash-prompt-command-messing-up-scroll-history-display
- http://stackoverflow.com/questions/4133904/ps1-line-with-git-current-branch-and-colors#comment4459222_4133922
Simplify .gemrc
Enable bash completion for the `g` alias (for Git)