Merge pull request #49 from Puuhinen/master

LC_ALL=C for all machine readable `date` output
$preview_url for those who writes posts locally before uploading them
one forgotten translated string template
make rebuild_tags() optionally accept 2 lists (of filenames and tags)
tags_in_post() to list all tags referenced in one post file
posts_with_tags() to list all posts referenced by several tag files
use new functions

also bugfix: leave only unique filenames in rebuild_tags()
don't rebuild tags if they were not involved at all

(otherwise posts_with_tags would endlessly freeze)
clean_filename in RSS links
Merge pull request #50 from Lex-2008/small-fixes/3

Small fixes/3
proper check for empty variable
fix typos in comments
Don't ask for preview - just show URL for preview
use markdown by default (if available) when posting with `bb.sh post`
use file extension when posting with `bb.sh post file.ext`

but let users override it with `bb.sh post -html file.md`
help text
Merge pull request #52 from Lex-2008/rebuild-less-tags

Rebuild less tags
Merge pull request #53 from Lex-2008/small-fixes/4

Small fixes/4
Updated README with markdown references
Updated version and contributors