Add zeus to list of gem defaults.
git find [gf] for nicely formatted, easy git-grep on commit tree.
An attempt to add stuff to script/bootstrap for new installs.

Ideally the goal is you clone dotfiles & run script/bootstrap, then
everything works.

At least the script/bootstrap should keep fairly up to date with changes
outside of the main Rakefile, even if it isn't tested.

This mainly adds the setup for base16 theme - which finally fixes the
problem of unreadable symlinks etc in shell (or hideous green in vim...)
Remove unneeded elements of the zsh theme to speed it up.
Use 256 colors with base16 for better compatbility with grc etc

GRC is the generic colouriser, and it doesn't play too well with the
non-256 color schemes.

Also even basic stuff like symlinks were broken before.  Finally a fix!
Set the custom agnoster theme rather than editing the oh my zsh one.