Implement all four base rulers (for Python)

[benjaminwoods]

Implement all four base rulers. Current design:

• nero
  1. Tests must exist for all functions and classes, in any test file
  2. Callables must be explicitly imported at the module level, in the test module
• joan
  1. Average cyclomatic complexity < 15
  2. Max cyclomatic complexity < 20
• genghis
  1. Tests must exist for all function and classes, in a specific folder format
• cleopatra
  1. PEP 8 compliance
  2. No more than 1000 lines

The signature of ruler functions also needs cementing.

[benjaminwoods]

Signature is a bit better now:

def some_ruler(path, name, testdir, language):
    # Do something
    pass

where:

• path is a pathlib.Path to a source file
• name is a string with the global name of the object
• testdir is a string with the relative path to the test directory
• language is a dict with info about the programming language

Still may change this to (path, name, language, **options), but this is fine for now.