Combinatoric Cheatsheet

A combinatoric cheatsheet. It include methods names and a short
description.
Merge branch 'master' of https://github.com/Mba7eth/sympy into comb_cheat
Updated Makefile for combinatoric cheatsheet.
Make Egyptian fractions a little more robust.

Add checking for negative arguments, and arguments > 1
Add check for legal input in egyptian fraction.

Reject numbers outside of (0,1), instead of trying to handle them.
Add Golomb's method for Egyptian fractions.
Use harmonic method for Egyptian fractions

Sum divergent series for values > 1.
ImageSet: added a method for intersection
S.Integers: added _eval_imageset method
Remove automatic evaluation
Added conversion to NNF
Add equals to boolean
Changed is_literal
Added tests
Fixed issues with Logical Atom
Fixed issues with count_ops and assumption
Changed count_ops and is_literal
Merge pull request #7432 from hargup/comb_cheat

Comb cheat
Merge pull request #7573 from clsn/egyptians

Make Egyptian fractions a little more robust.
Restructured Xor's __new__ method