add assert to grammar

[Stephen Siegel]

Add a rule for a regular assert statement to the grammar. It should be transformed exactly like a #pragma TASS assert, so no need to change anything else other than the grammar.

Rationale: the only reason for #pragma TASS assert is there are TASS expressions which are not regular C expressions (forall, etc.) But for assertions that do not require these special constructs, an ordinary assertion can be used, and TASS should check all ordinary assertions in a program as well as the ones marked with the #pragma.

[bperry]

Added an additional rule in the grammar that behaves exactly as the pragma assert without requiring the pragma.