1. Added a DCG grammar for RFC 2396 (URIs).
2. Updates to the DCG modules.

* [DCG_ASCII,NEW] Add crosshatch//[0,1].
* [DCG_ASCII,FIX] single_quote//[0,1] was not exported.
* [DCG_ASCII,EXT] alpha_numeric//[0,1] now uses code_type/2 (extends beyond the ASCII characterset.
* [DCG_CARDINAL,SC] Simplified the API a lot: removed arguments.
* [DCG_CARDINAL,SC] Reduced code size by reusing a predicate with meta-calls for converting arbitrary whole numbers to the decimal format.
* [DCG_CARDINAL,SC] Simplified the implementation of [un]signed_number//1.
* [GV_DCG,SC] Simplified the implementation of GraphViz identifiers, variants 1 and 2.
* [MATH_EXT,NEW] Added number_length/3 which allows an arbitrary radix to be set.
* [RFC_2396,NEW] Implemented almost the whole standard (excluding relative URIs) using DCGs.
* [RFC_2396,FIX] Changed the order os several DCGs, greedy style parsing.
* [RUN_EXT,EXT] Added the use of settings to register the programs to use for processing certain files (unfinished).