Make + and * universally associative/distributive; use +. and *. for Real

[jasone]

Basis currently uses the +, *, etc. operators for both integer and real types. However, there are compelling static and dynamic optimization opportunities if these operators are universally treated as associative and commutative. Operations on Real.t cannot in general be treated as associative and commutative, because re-ordering operations can affect the degree of precision loss. Therefore, we need to provide special operators for Real.t, +., *., etc., that are not subject to the same suite of optimizations. We could provide both set of operators for Real, but that may not be worthwhile because it exposes the programmer to the risk of accidentally using the associative/commutative variants and getting numerically unstable results.

[jasone]

The integer types have a // function which produces a real result. Although not strictly related to the + vs +. distinction for real, it may also make sense to rename // to /. as a clearer indication that the function is floating-point-related.