Use doubles instead of floats

All of the properties are doubles and we upcast when sending events
anyways, so just make everything doubles
Avoid warnings with WebKit2 in `snapshot`
Cast the decision in WebKit2
Add missing brace
Minimize the number of paths for returning
Set the io_loop to NULL after destroying
Free I/O resources
Always free the path memory
Don't app_cache_directory in WebKit2
Make webkit_view available in WebKit2
Return TRUE from accepted_languages in WebKit2