Initial attempt at supporting coveralls.io

This adds support for [coverage reports in Travis CI](https://coveralls.io).
You can see an example [here](https://coveralls.io/builds/429609).

I've included a bash script which does the proper coverage exclusion logic, but I fear my bash-fu might've let me down there as it's quite ugly.

You can run through all the steps in that script except for the last one to try it out locally. It should give you something like this at the end of your tests run:

```
...
      ✓ verify timezone validation 
      ✓ verify isGlobalAdministratorUser validation 
      ✓ verify isArray validation 
      ✓ verify isBoolean validation 
      ✓ verify isShortString validation 
      ✓ verify isMediumString validation 
      ✓ verify isLongString validation 


  861 passing (3m)


Done, without errors.
=============================================================================
Writing coverage object [/private/tmp/Hilary/coverage/coverage.json]
Writing coverage reports at [/private/tmp/Hilary/coverage]
=============================================================================

=============================== Coverage summary ===============================
Statements   : 86.05% ( 13160/15293 )
Branches     : 73.31% ( 4703/6415 )
Functions    : 89.43% ( 2674/2990 )
Lines        : 86.06% ( 13149/15278 )
================================================================================
```

I'll probably need to add a couple of things to get this fully working, so please ignore any failures this produces (for now).