better TIMEZONE comment, Fix #689
v6.0.4
Add a tags plugin to manage the tags used in the site.

Currently has the following features:

 - List all the tags (alphabetically or based on occurence frequency)

 - Replace multiple tags with a single tag, given a list of posts

 - Run the merge command in a test mode, to see the output before
   modifying a post.

This plugin is inspired by [jtags](https://github.com/ttscoff/jtag)
Flakes cleanup.
Add tests for list and merge features in tags command.
Use comma separated list of tags for tags --merge
Add --add and --remove options to the tags command.
Use post.tags instead of post.alltags to prevent reordering tags.
Add --sort option to the tags command.
Improve usage help.
Add --search option for tags command.

Currently does a basic term in tag and re.match.
Change the files only when tags have changed.
Commit missing tags test file.