Adds --debug flag to conversion script

[schuylermartin45]

Adds a --debug (and -d) flag to the conversion script. This flag prints debugging output to STDERR. For now it prints the initial parse-tree and the post-conversion parse-tree.

I've been using this strategy informally for months to determine if a bug is caused by an incorrect parse tree or a failure of the rendering function.

This PR also raises the unit testing coverage minimum to 80%. This should have been raised when the project was ported to conda-incubator.

Here's a sample debug output of a parser instance:

--------------------
RecipeParser Instance
- Variables Table:
{
  "name": "boto",
  "version": "2.49.0"
}
- Selectors Table:
  [py2k]
    - asadmin -h -> /test/commands/0
    - taskadmin -h -> /test/commands/2
- is_modified?: False
- Tree:
/
  |- package
    |- name
      |- {{ name|lower }}
    |- version
      |- {{ version }}
  |- source
    |- fn
      |- {{ name }}-{{ version }}.tar.gz
    |- url
      |- https://pypi.org/packages/source/{{ name[0] }}/{{ name }}/{{ name }}-{{ version }}.tar.gz
    |- sha256
      |- ea0d3b40a2d852767be77ca343b58a9e3a4b00d9db440efb8da74b4e58025e5a
  |- requirements
    |- host
      |- python
    |- run
      |- python
  |- build
    |- number
      |- 0
    |- script
      |- python setup.py install
  |- test
    |- commands
      |- asadmin -h
      |- s3put -h
      |- taskadmin -h
    |- imports
      |- boto
  |- about
    |- home
      |- https://github.com/boto/boto/
    |- license
      |- MIT
    |- summary
      |- Amazon Web Services Library
    |- description
      |- ['Boto aims to support the full breadth and depth of Amazon Web Services.', 'NOTE: Boto3, the next version of Boto, is stable and recommended for', 'general use.']
    |- doc_url
      |- http://docs.pythonboto.org/en/latest/
    |- doc_source_url
      |- https://github.com/boto/boto/blob/develop/docs/source/index.rst
    |- dev_url
      |- https://github.com/boto/boto/
--------------------

[beeankha]

TIL about starmap()! 🤩