Setup package ci versioneer

[znicholls]

This adds the bits to create a Python package from the code, namely:

• continuous integration with Travis (needs to be enabled by @RNourshargh, see https://docs.travis-ci.com/user/tutorial/)
• code coverage with codecov (needs to be enabled by @RNourshargh, see https://docs.codecov.io/docs/quick-start)
• tests (not passing at the moment, will pass them once CI is running)
• versioneer (makes doing version tracking super easy, it just uses the git tags)

[RNourshargh]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@a1d7ad6). Click here to learn what that means. The diff coverage is 100%.

@@           Coverage Diff           @@
##             master     #1   +/-   ##
=======================================
  Coverage          ?   100%           
=======================================
  Files             ?      2           
  Lines             ?      8           
  Branches          ?      0           
=======================================
  Hits              ?      8           
  Misses            ?      0           
  Partials          ?      0

Impacted Files	Coverage Δ
src/cavitysim/utils.py	100% <100%> (ø)
src/cavitysim/__init__.py	100% <100%> (ø)

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Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update a1d7ad6...aa567f6. Read the comment docs.

[znicholls]

tests are now passing, good to go @RNourshargh