This adds some features as well as drops a few unneeded things. In no
particular order:

* Generates up to three bazel targets per element
  * a cc_library for static and shared libraries
  * a py_library for
  * a filegroup with all the files (except excluded, see below) to be
    used as a data dependency
* No longer includes C/C++ source files in cc_library
* No longer generates cc_import targets
* Allows using split rules to select which files are included/excluded
* Includes the files from its direct dependencies in the artifact (so
  the artifact can be used directly by bazel)
* No longer allows runtime dependencies
* No longer allows sources (which were ignored previously anyway)
* Always rebuild when dependencies change (even in non-strict mode)