Install `karma` and `yo` with npm

Globally install two additional node packages.

Karma is a JS unit test runner.
Yo is a command line tool for scaffolding projects.
bash: export PhantomJS's `bin`

PhantomJS is installed with Homebrew. This exports the package's `bin`
for other software (like Karma) to be able to run PhantomJS.
git: make `who` alias more useful

Make this alias expose people who have recently been active committers.
It will display an ordered list of people who have made commits in the
last 3 months. All merge commits are ignored.