add pug support

[Sys0MKNR]

This pull adds pug support. It is kept in a seperate file to make the process of removing jade easier. If this pull gets accepted also my pull in the electron/electron-compile repo needs to be accepted to enable pug support. This just adds 'text/pug': 'pug' to the typesToRig object in src/rig-mime-types.js.

[naderm]

Bumping this!

The current jade version relies on an old version of uglify-js that is vulnerable to the security exploit CVE-2015-8857

(jade@^1.11.0 > transformers@^2.1.0 > uglify-js@~2.2.5)

[graup]

+1 What do we need to do to get this merged?

[j-fan]

Would also like to see this merged :)

[Tenrys]

Isn't jade a little bit outdated since the rename? Would be nice to finally be able to use pug instead.