sfeed: Update to 1.2

Changes:
1.2
---
Fixes:
* sfeed parser: extend the time range to atleast 64-bit (long long).
* sfeed parser: allow leap second like 23:59:60 (RFC2822 Section 3.3).
* sfeed_curses: pedantic fix for UB with an empty URL file (qsort and bsearch).
* sfeed_curses: fix a compile warning with tparm() on some systems.

Features:
* sfeed_atom: add category field(s).
* sfeed_curses: add feature to go to the next bold row and previous bold row
with J and K.  This is useful to quickly jump to the next new item or new feed.
Thanks to IanJ for the suggestion and feedback!
* sfeed_content: allow to set HTML converter with env variable $SFEED_HTMLCONV.
For example: SFEED_HTMLCONV="w3m -I UTF-8 -O UTF-8 -T text/html -dump"
* Add compile-time option to improve output on dumb non-UTF8 terminals
(-DSFEED_DUMBTERM).

Misc:
* Documentation improvements to the man page and a sfeed_download example in
the README: this is a parallel downloader/extractor example script.
* Code-style improvements.

(leot)