Allow exclusion of this/self

It would be nice to be able to not show the `this/self` (sometimes called the "passed object dummy argument") argument in the generated documentation for type bound procedures. Also allowing it to not have a comment.

As you should never be passing this argument to a type bound procedure on use it is redundant and confusing to include it in the generated API docs.

The issue names no files, tests, or entry points; begin by tracing how FORTRAN type-bound procedures are parsed and rendered in the documentation generator. Done means the generated API documentation can omit the `this/self` argument and optionally omit its comment, with coverage for both settings.

Written by the indexing model from the issue text.