This fixes the numerically unstable math.intersect() for the 2
dimensional case by computing whether the determinant is within
config.epsilon instead of a hard equality check.
- Added intersect.js file in lib/expression/docs
- added an entry in the index.js file in expression/docs
- modified intersect.js to give appropriate error messages
- added an entry in lib/math.js so that the test case file could find
the function
- wrote the test cases for intersect