Add option to not leading-space header titles

[wsnyder]

Per #157, Please add a style option to not add spaces on chapter headings.

Example where - is what it does now, and + is what I want to round-trip the same:

+****************
+Revision History
+****************
-******************
- Revision History
-******************

I confirmed a hardcode change of title() in docstrfmt.py to this does what I want:

        if overline:
            # section headings with overline are centered
            yield char * (len(text))
            yield text
            yield char * (len(text))