Add initial bazel build

[malkia]

This adds basic bazel support

No fuzzing, or sanitizers yet, but the ability to select json library and all other tests are in.

bazel test -k ...

This would select the nlohmann json library. To select another, for example rapid json, use this:

bazel test -k --//:json=rapid ...

The other options are: jsoncpp and nlohmann (the default)

When used as module dependency, you should fully qualify - e.g. --//@cppdap:json=<library>

common --//@cppdap:json=rapid

Place above in your .bazelrc file, and it'll set rapid json as the default choice.