Since `simcells.v` uses consistent formatting we can handle it specifically to help tidy up sphinx warnings about the truth tables, and instead chuck them in a code block which when printing to rst.
Also has the side effect that rst code blocks can be added manually with `//- ::` followed by a blank line.
Include Source file and line number in SimHelper struct, and use it for verilog code caption in rst dump.
Also reformat python string conversion to iterate over a list of fields instead of repeating code for each.
Allows for more expressive code when constructing help messages for cells.
Will also move extra logic in parsing help strings into the initial python parse instead of doing it in the C++ at export time.