strbuf.h: reorganize api function grouping headers
The original API doc had something like:
Functions
---------
* Life cycle
... some life-cycle functions ...
* Related to the contents of the buffer
... functions related to contents ....
etc
This grouping can be hard to read in the comment sources,
given the "*" in the comment lines, and the amount of text
between each section.
Instead, let's make a flat list of groupings, and underline
each as a section header. That makes them stand out, and
eliminates the weird half-phrase of "Related to...". Like:
Functions related to the contents of the buffer
-----------------------------------------------
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>