ENH: Add code coverage support

Add code coverage to .travis.yml via https://coveralls.io

Fixes #301

                          ________
                         | ______o|
         _______________ ||__---_||
        |  ___________  || ______ |
        | |           | |||______||
        | |#scikit-bio| ||--------|
        | |           | ||      O |
        | |           | ||      | |
        | '-----------' ||      | |
        |_____________-_||      | |
          __/_______\__  |::::::::|
         ________________'-.__
        /:::::::::':::'::\ .\\\---.
       /::======::: .:.:::\ \\_)   \
       `""""""""""""""""""`  '-----

Art via:
http://www.geocities.com/spunk1111/computer.htm
ENH: Add coverage badge
ENH: Add support for test option on setup.py
ENH: Add .coveragerc file for coverage.py

Wear it: 👖
ENH: Ignore __init__.py files
MAINT: Remove -after_success section
BUG: Change skbio.test to nose.collector

Thanks NumPy!!
ENH: Add default settings to .coveragerc

Ignore a lot more things that are not useful.
ENH: Add combination of code-coverage commands

Fixes #305
Merge pull request #305 from ElDeveloper/coverage

ENH: Add code coverage support