* Simplified & tightened all_close_f parameters

Removed specification of mantissa bits for all_close_f in favor
of just specifying tolerance bits. Tightened up all_close_f default.
Fixed LRN unit test which had insufficient result precision to pass
tighter all_close_f tolerance.

* Addressed PR comments.

Reworked mantissa bit and tolerance constants.
Clarified and improved graph comparison tolerance calculation flexibility.
Clarified unit test tolerance testing.