Refactor defined MATH_BIGINTEGER_ constants into class constants.
Move in-code comments to property doc blocks.
Add #@+ block for properties used by internal implementation.
Merge pull request #544 from bantu/cnelissen-BigIntegerConstantsFix

Refactor defined MATH_BIGINTEGER_ constants into class constants.

* bantu/cnelissen-BigIntegerConstantsFix:
  Add #@+ block for properties used by internal implementation.
  Move in-code comments to property doc blocks.
  Refactor defined MATH_BIGINTEGER_ constants into class constants.