Add 'invert' function

Compute the inverse of an element of ℤ[x]/(n, x²-bx-c).
Tests for computation of x^s
Test the computation of x^s itself for n=3 mod 4
Change measurements file format, add new data for n=1 mod 4
Test 'invert'
Properly free memory at the end of each test
Reformat code
Fix 'invert' function
Properly handle n≡3 mod 4
Add macros to simplify code involving polynomials
Use new macros for the testing code
Slightly change a few tests
Move powm to the tests
Fix a memory leak
Add run time measurements
Remove unused variable
Refactor code concerning input sets
Code cleanup
Analyse run time standard deviation
Add more measurements