Fix: Twip::get_parameters

This function uses an unreliable method to get parameters in request
string. It always returns empty array on my own virtualhost.

Since we don't actually need to distinguish between parameters in query
string and POST body, we can just use `$_REQUEST` global array.
Fixed: pass only the `path` parts of to the filter

I didn't realize the query string was passsed into the filter...
Mod: feature improvement

Twip::uri_fixer should be removed in the future since T mode and O mode
should use different rules of fixing.

Also added `Twip::parse_entities` in the JSON response.