* CHANGE .travis.yml so that commands for different purposes (e.g. getting
dependencies, building, testing) are in separate config lines and sections.
* CHANGE .travis.yml to use their mechanism for installing dependencies via
apt. [0] This also allows us to not need sudo (the "sudo: false" line).
* CHANGE Travis CI tests (the "script:" section) to build and run tests in the
same manner as Jenkins (i.e. with --enable-fatal-warnings and
--disable-silent-rules and run `make check`).
* ADD Travis configuration to do all the target builds with both GCC and clang.
* ADD make flags to build with both of the cores available.
* ADD notifications for IRC, and configure email notifications (to the author
of the commit) only if the branch was previously building successfully and
the latest commit broke it.
* ADD the ability to run the Travis build matrix for OSX as well, but leave it
commented out by default (because it takes roughly ten times longer, due to a
shortage of OSX build machines).
* ADD Travis config option to cancel/fail the build early if one target has
already failed ("fast_finish: true").
* ADD comments to describe what our Travis config is doing and why it is
configured that way.
[0]: https://docs.travis-ci.com/user/installing-dependencies/#Installing-Packages-on-Container-Based-Infrastructure)
Installs dependencies (including rust) and runs the existing test suite.
TODO: Introduce build matrix utilizing the rust toolchain to run test
suites both with and without the rust components.
