Implement is/2
Run TAP tests that don't have names

library(tap) recently introduced the ability to write tests that have
no name.  The test is described as a term which represents both the
test name and the test logic.  Support those kinds of tests in the
Golog test suite.

This requires us to recognize when library(tap) is imported so that
only those terms after the import are considered as tests.
Implement term comparison predicates

The implementation is based on term.Precedes() which was already
implemented for msort/2.  The ISO test suite found a couple problems
with our comparison implementation:

Rationals must always report themselves as floats.  Otherwise, 1.0
behaves like an integer which causes `1.0 @< 1` to fail.

When two number terms are numerically equal, ISO and SWI-Prolog both
sort the floating point number first.  This seems silly to me, but I
see no compelling reason to buck the consensus here.