#101 Add Travis yaml file

[msimet]

This is a PR to add the Travis yaml file to the repository. This will probably need tweaks to the yaml file, but I won't know what they are until Travis runs, and it won't run until I make a PR!

[msimet]

And, right, we'll need to wait for PR #104 before this will run successfully!

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@e9193b9). Click here to learn what that means.
The diff coverage is 72.5%.

@@            Coverage Diff            @@
##             master     #107   +/-   ##
=========================================
  Coverage          ?   26.35%           
=========================================
  Files             ?        9           
  Lines             ?     2360           
  Branches          ?        0           
=========================================
  Hits              ?      622           
  Misses            ?     1738           
  Partials          ?        0

Impacted Files	Coverage Δ
stile/file_io.py	60.8% <55.55%> (ø)
stile/stile_utils.py	66.66% <71.42%> (ø)
stile/treecorr_utils.py	56.66% <93.33%> (ø)

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