Simplify font handling:

Simplify font handling:
1. Inherit the font attribute from the parent box, such that iteration
is no longer required to find the current font.
2. For well-known function name tokens, do not insert an EQN_LISTONE
box into the AST; simply set the font attribute of the text box
itself that contains the name.

Also improve word splitting of unquoted strings in default font mode:
3. Split between numbers and punctuation because both will soon get
different HTML markup.
4. Do not split between letters.  With the newly ubiquitious font
attributes, all formatters will be able to figure out what to do
without putting each letter into a separate box.