new bazel rules for frege

[P. Oscar Boykin]

 I recently implemented these bazel rules for frege:

https://github.com/johnynek/gottlob

They allow you to depend on any other java/scala code or vice-versa.

I haven't used them much, but they may be interested to people interested in reproducible build, which bazel gives you.

There is one efficiency issue: since bazel uses hashing to determine if files have changed, the timestamps embedded means you get a full rebuild every time:

see issue:

https://github.com/Frege/frege/issues/247

I have not yet had the time to send a PR to add the option to frege to put a constant value in the timestamp slot which will make things reproducible.

[Ingo W.]

Hi Oscar,

thx for the work!

Looking for your PR. 

(Still I can't see how Bazel would know which frege files would have to get recompiled if some class files changed.)

Best regards, Ingo