Bazel build support

[reddaly]

Would the authors be interested in accepting a PR for building mdbtools with bazel? I have a branch with suport for building some of the mdbtools binaries: https://github.com/reddaly/mdbtools/tree/bazel

Bazel makes it pretty easy to build mdbtools reproducibly without installing all the deps.

Example commands that build and run some of the
mdbtools utilities:

bazel run //src/util:mdb-tables -- --help
bazel run //src/util:mdb-json -- --help

The approach in my repository might be too much of a hack for the official repository. Some .h versions some .h.in files are included in the repository for now. That could be cleaned up if you would accept a PR with bazel support. otherwise I will probably leave that repo in its working but unsophisticated state.