Replaced GNU-specific init_random_seed routine in maths_module.f90.

With the release of gfortran v7, the random number routine was changed
so that the intrinsic random_seed() function call would generate a new
sequence every time. This rendered the GNU-specific initialization
redundant, although the previous workaround code can still be found
in the file gnu_v6_init_random_seed.f90.

Added results of corfun.py test runs

Added Python version of qmc_pi_lj. Extended documentation.

Added Python versions of mc_chain_wl_sw, mc_chain_nvt_sw and wl_hist.…

… Made corresponding changes to documentation and Fortran versions.

Minor edits only

Transferred grint_data.zip to data repository

Final changes ahead of first release