Much improved SXP generation, list errors and fixed some read_character issues

Improvements for most everything, including mal-formed list detection, read_character support for lisp and scheme escapes, and improved the SXP output generation.

I also needed to change RDF::Literal generation to use the string format for integer, boolean and so-forth, if it is valid; this ensures that SSE is output with the original input formats, needed for lexical validation.

The only real remaining thing is support for vectors, which doesn't really interest me, but would be good for completion; then we could probably release it as a 1.0 release.