bugs fixing

Current plugin implementation has several issues, like:

* doesn't work with current phile version
There is a small problem in phileCMS, with leading and following slash in urls now. 
`$data['uri']` is usually something like `tag/php`. So, `dirname($uri)` would be just `tag` for `tag/php` and a `.` for `tag/`. As result, plugin doesn't work at all (I don't know how it works on your server yet :D )
 
* broken back-compatibility
plugin override `page.meta.tags` variable, which is default to raw-meta-string from a `*.md` file. Some plugins (existing and future) can relies on that, in this case, phileTags will bring a headache :)

* doesn't allowed to mix tag-separator 
`Tags: tag1,tag2` and `Tags: tag1,  tag2` are different. I think, it should be the same

* not suitable for tags with spaces (`Tags: by first tag, my second tag`) and non-latin tags
because current_tag will contain urlencoded characters

* outdated README
The example-code is for pico and isn't very suitable for new phile and plugin users.

So.. I have fixed this issues.