Create custom diff tool to compare stub contents

Context:
- Create a tool to analyze loose equivalence of the stubs in two
  directories
- The tool can analyze strict equivalence of the directories of the
  stubs in two directories
- Analyze text to compare loose equivalence of the stub contents; Add a
  functionality to pass `skip_words` as arguments, which are optional
  list of words used to signal the tool which words are not considered
  diff
- The tool can be locally used to compare stub contents, and does not
  contribute to build process

Test: m
Change-Id: I74563a9a24ecdde939be2ce37b9096a9aeb4920a