Refine LazyRequest equality semantics

LazyRequest's are now only equivalent to other LazyRequest's with
identical underlying raw maps. The RawAccess interfaces 'raw' and
'realized' methods can be used for deeper comparisons with raw maps.

DerefingMapEntry's equality is not defined (at present). 'seq' should be
used to obtain a realized vector for comparison.

Bonus: Added docstrings for creation functions, and updated tests to
match new semantics.