Change zinc to support tests

Adds the required cfg attributes to build with --test and mocks out
all the functions with inline asm.

  - [ ] Get zinc to build with test
  - [ ] Add test to Rakefile and travis
  - [ ] Refactor inline asm (move to designated area, dummy with `fail!`
Merge pull request #49 from bharrisau/first-test

Change zinc to support tests