Teach zeroNumFloat about "0."

In particular, it should probably parse as 0 with a '.' still pending.  This
should have been in with 'Tweak decimalFloat handling.'
Missed a 'try' in buildExpressionParser

This fixes my previous patch, 'Allow overlap between prefix and term in
buildExpressionParser', to allow terms in the space of prefixes.
Merge pull request #8 from nwf/master

Some more tweaks for your consideration