Base primitive improvements

[brucemiller]

Fixes various little fidelity problems that turned up while playing with plain.tex.

• recognize more font names
• initialize State more like INITEX does (UC,LC codes, etc)
• a bit better with \nonscript, '\fam`,
• make \write expand in the special \the style ('XGeneralText` parameter type)
• Various primitives, '\mathopen`, etc, should digest args
• Fixup \left,\right processing to digest args while still grouping between them.