Enable doctest, improve type annotations and documentation in helperfuncs.py. Also:

* Simplify some examples to make them testable, and fix some incorrect examples.
* Discourage use of `input_list`, `output_list`, `register_list`, and
  `wirevector_list`. They've been removed from the documentation. List
  comprehensions are easier to read and don't expand the API.

Author: fdxmw

docs/helpers.rst

@@ -46,14 +46,6 @@ Control Flow Hardware
     :undoc-members:
 .. autofunction:: pyrtl.helperfuncs.match_bitpattern
 
-Creating Lists of WireVectors
------------------------------
-
-.. autofunction:: pyrtl.helperfuncs.input_list
-.. autofunction:: pyrtl.helperfuncs.output_list
-.. autofunction:: pyrtl.helperfuncs.register_list
-.. autofunction:: pyrtl.helperfuncs.wirevector_list
-
 Interpreting Vectors of Bits
 ----------------------------