Implement LU decomposition
Add tests for LU decomposition
Implement SymPy version of fraction_free_LU
Implement QR factorization
Merge branch 'master' into Matrix_Decompositions
Add new test
Add brackets when printing a `Rational`
Merge branch 'Fix_#204_print_error' into Matrix_Decompositions
Fix `mul` simplification
Remove the `for` loop inside `from_dict`
Implement LDL decomposition
Merge branch 'master' into Matrix_Decompositions

Conflicts:
	src/dense_matrix.cpp
	src/matrix.h
	src/tests/matrix/test_matrix.cpp
Added primesieve.org library
Add `mul` benchmark
Refactor `Mul::from_dict`
primesieve travis
Implement LDL and Cholesky decomposition
Comment out cholesky tests
Merge branch 'master' into Fix_Simplification
Remove commented out code