Merge #52

52: Refactor ToPrimitive range checks r=cuviper a=cuviper

This is a rebase and continuation of PR #28.  The primary benefit is that
floats finally check for overflow before casting to integers, avoiding
undefined behavior.  Fixes #12.

The inter-integer conversions and all of the macros for these have also been
tweaked, hopefully improving readability.  Exhaustive tests have been added for
good and bad conversions around the target MIN and MAX values.

Author: bors[bot]