Update heurisch.py

Reduced the number of permutations of mapping by not generating cases where mapping[-1] != x
Update heurisch.py

changed \t to 4 spaces(indentation correction)
Update heurisch.py

Optimized the number of permutations of mapping by not generating cases of the form mapping[-1]!=x
Update heurisch.py

Corrected the cases causing assertion failures
Update heurisch.py

indentation error corrected
Update heurisch.py

Solved errors caused because of special functions like fresnels
Update heurisch.py

removed whitespaces in line 253
Update heurisch.py

Removed all whitespaces
Update risch.py

Changed the hermite's reduction from quadratic version to Mack's linear version. This requires only m-1 linear reduction steps unlike the former version which was quadratic in m. Also no decomposition of f or square-free factorization of its denominator is required reducing the time-complexity further.
simplified the expressions in the test file:risch.py for test cases of hyperexponential and hermite_reduce