Emit a friendly error when fig.yml is missing

I keep doing this by accident, so I'd rather not see the stack trace.
Merge pull request #4 from tomstuart/be-friendlier-about-missing-fig-yml

Be friendlier about missing `fig.yml`
Add Travis CI
Fix Python 2.6
Add Travis badge
Fix Python 2.6
First version with python3 support.

 * Moved requirements*.txt files to proper spec definitions in setup.py
 * Added a new fig.compat module to store some compatibility code
Added tox file
Fix exception alias syntax
Use print function
Add future import for print function
Add texttable compat module that is py3k compatible
More future imports for safety
e.explanation a 'str' object
Add unicode_literals to main module
Add Python 3 and PyPy to .travis.yml
Put requirements back in .txt files

Read-only FS in travis
Allow Python 3 to fail

docker-py is broken
Very basic CLI smoke test

See #8.
Failing (on 2.7, at least) smoke test for 'fig ps'

See #8.