TexCommon

This cleans up newline handling in the whitespace parser:

Newlines are not treated the same as other whitespace any more and are
only allowed after the functor expression and between individual
morphism points.

By doing this, we get a less surprising grammar for parsing ("x: { y:"
would never try to parse the "y:" as the start of a new definition)
and can speed up the hot path (a single space character) considerably.