Improve benchmark runner

Make it possible to select certain sets or algorithms to run, rather than
using comments to disable these.
Remove all measurements concerning the Frobenius test
Simplify labels of fitted functions in multiplications plot
Add some documentation
Fix a bug in sigma, still not entirely correct
Add another comment
Use sigma for the n≡3 mod 4 case
Add function to calculate x^k for some k using Lucas sequences

The code is currently incorrect.
Check more interesting number in test_frobenius_primelist
Disable temporarily unnecessary tests
Add a test to check whether sigma is correct
Add test for powm_x_lucas and fix Makefile
Disable some more tests
Replace right-to-left with left-to-right binary exponentiation
Change sigma to get rid of the temporary variable
Add documentation
Rewrite macro based tests
Test the RQFT on composites
Rewrite powm_x_lucas
Rename powm_x_lucas to power_of_x