Initial support for travis-ci

Here is some initial support for travis.

It doesn't build successfully at the moment (https://travis-ci.org/bharrisau/zinc/builds/24582373), `support/rake.rb` is pulling the newest master to build libstd which is incompatible with the current rust-nightly in the ppa repository. Looks like f128 was added to the git repo but hasn't appeared in the nightly build.

Not sure of the best solution, one option is to:

  - Extract the commit SHA from `rustc --version`
  - Clone mozilla/rust with depth ~100
  - Checkout the correct SHA before patching