set up better CI system

[ongardie]

LogCabin currently uses a mixture of Travis CI, pre-commit hooks, and a hookmatrix script.

The pre-commit hooks:

• + are pretty extensive
• - must be set up and configured on every dev box

Travis CI:

• + runs automatically when randos submit PRs
• + uploads new documentation to https://logcabin.github.io
• - runs only a subset of the pre-commit hooks
• - runs only one particular compiler version

hookmatrix script:

• + can run all supported compilers
• - requires a ridiculous number of compilers and libraries installed, only really supported on Diego's Thinkpad.

In the short term, I'd like to get to a point where all testing required to merge into master is automated and triggered by a GitHub PR. Longer term, I'd like to get to a point where all testing required for an official release is automated.

I don't have a concrete suggestion yet but will look around and think about this problem.

[ongardie]

travis-ci/travis-ci#979 (comment) suggests it's worth looking through Travis CI again in case it has some new features we can make use of.