Changed tol on Complex and Real field to None

Fixes simplification issue #7263. Added test to check issue in
test_simplify.
Fixed travis errors

Direct comparison of expressions lacks enough precision for ==.
Comparing numerically now with evalf().
Added non homogeneoous linear ruler eq
Corrected the documentation
corrected nameerror
Added trialset match in nonhomogeneous euler eq
Fixed the error coming due to Dummy
added simplfication of log function
undetermined coeff type solved
corrected all test cases
variation of parameters integral solved
Able to solve eq for symbolic coeff
Added separate method for nonhomogeneous euler eq Includes both undetermined coefficients and variation of parameters to solve nonhomogeneous euler equations
Implemented Mobius Function in residue_ntheory module
Reimplement mobius function as a class
Changed test to check abs(output - answer) < 1e-15
Merge pull request #7271 from skirpichev/issmob-dhruvesh

Implemented Mobius Function in residue_ntheory module
Merge pull request #7360 from jcrist/issue7263

Changed tol on Complex and Real field to None
Merge pull request #7290 from KDMOE/nonhomogeneous_euler_eq

ODE: Added non homogeneoous linear euler eq fixes #7172
Add support for finding the power set

This patch adds powerset() method to sympy.core.sets to find the
power set of a set.