rename USE_NUMERIC_ENTITY and change meaning

[Patrice Dumas]

Hello,

Right now, USE_NUMERIC_ENTITY means
     For HTML and XML.  If set, use numeric entities instead of ASCII
     characters when there is no named entity.  By default, set to true
     for HTML.

I think that it is not logical.  It would be better to name differently
that customization option, I would propose 'FALLBACK_TO_NUMERIC_ENTITY'
and change the meaning of USE_NUMERIC_ENTITY such that USE_NUMERIC_ENTITY
means:
     For HTML [and XML?].  If set, use numeric entities instead of named
     entities.  By default, set to false.

Would that be ok?  I do not think that it is an issue for compatibility
as I do not think that users ever wanted the former USE_NUMERIC_ENTITY
to be false.

-- 
Pat