Add coil / pystachio comparisons
Add ability to generate multiple JSON files
Build jsonnet with bazel and BUILD files.

Details:
- Breaks Makefile. Sad trombone.
- Add bazel-* directories to .gitignore.
- Add WORKSPACE to designate bazel workspace root.
- Move source files into a subdirectory of the workspace root.
- Add tools/... directory that bazel needs to actually build anything.
  This part of the change copied nearly unmodified from
  https://github.com/google/bazel/tree/master/example_workspace.
Move test stuff from //test_suite to //src/testdata.
Merge branch 'build-with-bazel' of github.com:cdrichards/jsonnet into build-with-bazel