Fixed hardcoded tag filename prefix

the bug was that sed was expecting file content on stdin when didn't receive
any filename, and script was "frozen" when someone tried to edit a post
without any tags.

posts_with_tags() invoked sed with a hardcoded `tag_&.html`.
Changed to `$prefix_tags&.html`.

Small fixes/4

Rebuild less tags

but let users override it with `bb.sh post -html file.md`

Small fixes/3

(otherwise posts_with_tags would endlessly freeze)

also bugfix: leave only unique filenames in rebuild_tags()

LC_ALL=C for all machine readable `date` output

The script used to have LC_ALL=$date_locale for all calls to `date`.
However, this is undesirable for when $date_locale is non-English and
dates need to be machine readable, e.g. for `date --date=...` and
when generating RSS feeds.

Allow utf-8 filenames

* force to lowercase or not
* what symbol to use instead of space
* what symbols to allow in filenames (makes bashblog more utf-8 friendly)

test markdown before editing *.md files

do not iterate over ls output where possible

updated original link

Save md