Fixed transparent elements list.
Moved transparent out of category because it's not a category.
Renamed *_set to *_init to make it clearer.
Renamed Ando_Regex::is_matchable to the more standard ::is_valid.
Added all code I developed years ago for counting capturing groups.
Added many TODOs to improve / fix Ando_Regex::substitute_variables.
Started adding attributes. (wip)