docs: Woefully inadequate docstrings

[johnandersen777]

We are seriously lacking in our docstrings.

https://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_numpy.html#example-numpy

https://intel.github.io/dffml/master/api/repo.html

[johnandersen777]

I added the first examples here:

• https://intel.github.io/dffml/master/api/db/sql.html

• dffml/dffml/db/sql.py

  Lines 107 to 122 in 8c5dfa3

  	Creates insert query. Keys in ``data`` dict correspond to the columns in
  	``table_name``.
  	Parameters
  	----------
  	table_name : str
  	Name of the table.
  	data : dict, optional
  	Columns names are keys, values are data to insert.
  	Returns
  	-------
  	query : str
  	``INSERT`` query
  	parameters : tuple
  	Variables to bind