initial commit
add README
zshrc: use $HOME when setting default $HOME_GITDIR
README: add alternate strategy
zshrc: fix conditional setting variables
update git completion/prompt to v1.8.5.5
vim: add HiLinkTrace module
ipython: import useful modules and itertools functions
zshrc: always use our git-completion.bash

The most recent version of _git (aka git-completion.zsh) has changed behavior,
preferring the system's git-completion.bash over our own.  This commit forces
_git to use our version, which we know is always in sync with _git.