Bump master to development release 2.11.0

To anybody confused this is not the next stable release, it is just a way to differentiate master
from the 2.10 branch and next stable will be 2.12.0 similar to Gnome's versioning scheme.
Update readme.md
Update badges in readme
Use GFile API in gtkutil_check_file instead of stat/access.

The latter functions expect codepage-encoded filenames on Windows but GLib's API returns filesystem-encoded paths, which on Windows are UTF-8. GLib API should be used to deal with GLib API results.

Also fixed leaks in two of the callers of gtkutil_check_file()

Fixes #968
Merge branch 'master' of https://github.com/hexchat/hexchat
Fix DOMAIN and EMAIL patterns.