Remove TERM environemnt variable

Weechat has redraw issues with xterm-256color and requires
screen-256color.  Vim does not seem to be affected.
Remove foldlevelstart

I've noticed that I almost always immediately call zR after
opening files.
Map semi-colon to colon

One less keystroke.
Enable Airline tabline in the terminal
Add 'build' to Ctrl-P's list of ignored directories
Revert "Use Hemisu colorscheme"

This reverts commit b27829101575716dcc5eaddce29493c40de07ef1.