normalize versions and update changelog

readme says `Stable Tag: 1.4`
https://plugins.svn.wordpress.org/batcache/tags/1.4/readme.txt

readme in github says `Stable Tag: 1.2`

file says `Version 1.2` in 1.4 branch
https://plugins.svn.wordpress.org/batcache/tags/1.4/batcache.php

_i haven't diff'd files with what's on wp repo but i'd hope this repo would be currrent_

While you're at it fix the url too (rem extend/ slug) ;)

```
Plugin URI: http://wordpress.org/extend/plugins/batcache/
```