[WIP] Create tests for basic dub usage + bump compiler version to 2.065.0

So this was more useful than I previously thought...

It revealed 2 issues related to dynamic libraries, which is why it can't be merged yet also. The first one is #352 which prevent building dynamic libraries right now. The second one is that dependencies to dynamicLibraries used to trigger a this-is-not-implemented-yet error. Now, the dependency is just converted to a "library" dependency, which is a staticLibrary. Thanks to #352 I noticed it.

The code for .travis.yml seems to be the same than the one I wrote for vibe.d. Unfortunately, it suffers the same problem vibe.d had (aka, it should "exit 1" instead of "break"). And it was testing the "dub" in the system path (so the downloaded one, which is currently 0.7.21) anyway. So the unittests are useless ATM.

Lastly, why is "library" intended for ? I think it would be *super* nice to have a package that's marked as "library" build both dynamic and static library. This way, one can depend on a package either by library (which should be dynamicLibrary), by staticLibrary or dynamicLibrary.
Is there any precise guideline on how many versions dub supports, or does it depends on the compiler changes for each version ?
Currently, the build takes less than a minute. The among of daily push / PR is fairly low (10 a day over the past month at most). So even if supporting 2.06{4,5,6} would mean tripling the time, and we add a great amount of tests, there's little chance we would reach, say, 4h of total build time per day. This is ridiculous compared to [other projects](https://travis-ci.org/ldc-developers/ldc/builds).

So should I update this to support different versions, or just fall back to 2.064.2 ?