Create interface class for bathtub.

[williaml33moore]

Closes #127

• modified: src/bathtub_pkg/bathtub.svh

  • Implement new interface class, bathtub_interface.
  • Because we're implementing an interface class, methods had to become virtual.
  • Break include loops.

• new file: src/bathtub_pkg/bathtub_interface.svh

  • New interface class for bathtub.

• modified: src/bathtub_pkg/bathtub_pkg.svh

  • Removed step_attributes_pool_t typedef to its own file.
  • Why? I'm glad you asked.
  • It was responsible for a very tricky include loop.
  • The crux was that any file that needed something as innocuous as strings_t had to read this file, which meant it had to include step_nurture.svh, which turned out to be a six-degrees-of-separation nexus that led to a loop that could not be resolved.
  • The solution was to move step_attributes_pool_t out, with the express goal that bathtub_pkg.svh now does not include any other files.
  • Anyfile that requires a declaration in this file no longer inherits an unrelated include file with all its headaches.

• modified: src/bathtub_pkg/bathtub_utils.svh

• modified: src/bathtub_pkg/gherkin_document_printer/gherkin_document_printer.svh

  • Break an include loop.

• modified: src/bathtub_pkg/gherkin_document_runner/gherkin_document_runner.svh

  • This is the one file that actually requies step_attributes_pool_t, so this file includes it directly, instead of going through bathtub_pkg.svh.
  • Break an include loop.

• new file: src/bathtub_pkg/step_attributes_pool_t.svh

  • New file for a single typedef.
  • Seems extravagant, but that typedef is dependent on another include file that was causing trouble, so the "expense" of a new file that breaks an otherwise uncompilable loop is justified.

• modified: test/dependency_test.py

  • Test the two new files.