Add code coverage reporting to Travis CI

[mewmew]

(Creating dedicated issue for tracking this work. Comment originally posted in #117 (comment))

The Travis config may be extended to report the lint status of the project. For an example project using this approach, refer to the following goclean.sh script and travis config:

• goclean.sh (which is a fork of https://gist.github.com/h12w/0f22736320abe6be71ce).
• .travis.yml

The goclean.sh script reports issues from gofmt, goimports, golint, go vet, go test -race and go cover. Test coverage is optionally reported to https://coveralls.io/.

Note, the secure environment variable is an encrypted version of the COVERALLS_TOKEN environment variable. For a howto, see decomp/decomp#4 (comment).

[paked]

Harrison Shoebridge @paked 21:09
@otraore Is this [coveralls] done: #295
I've seen coveralls around the place, so I assume so?

Ousmane Traore @otraore 21:09
It is done BUT
there’s an issue on coveralls side and our badge
as for reporting it’s done in the PR and the page as well
But this is a bug others are experiencing as well.
So you can close the issue.

Edit(@otraore): Fixed by #301