Tweaks to codecov setup

[willfurnass]

• Try using Python codecov uploader
• Add check in .travis.yml for existence of .coverage file
• Add fairly generic .coveragerc config file

Goal is to get the codecov uploader to find and upload the data in .coverage; to date it reports not being able to find any coverage data to upload (#157 (comment))

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@77def8c). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #185   +/-   ##
=========================================
  Coverage          ?   21.21%           
=========================================
  Files             ?        6           
  Lines             ?     8376           
  Branches          ?     1768           
=========================================
  Hits              ?     1777           
  Misses            ?     6544           
  Partials          ?       55

---

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 77def8c...f12e669. Read the comment docs.