Small code formatting.
Renamed Regex::tmp_fixed_positions to Regex::tmp_new_references.
Renamed Regex::fix_template_backreference to Regex::fix_template_numbered_backreference.
Renamed Regex::fix_variable_backreference to Regex::fix_variable_numbered_backreference.
Added support for (absolute) lexical numbered backreferences: First part of issue #5.