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
rename include guard macros
rename to hpp
merge from hexchat/master
remove build badges that don't apply to this repo