renames constants_mod.f90 to shared_par.f90
uses module shared_parameters in shared_par.f90 for Par_file parameters, simplifying calls to read_parameter_file()
updates CPML routines for convolution and pml_compute_memory_variables_acoustic for slightly faster calculations
updates FORCE_VECTORIZATION for fluid/elastic parts; adds --enable-debug and --enable-vectorization to configuration script; updates flags.guess; adds file setup/config.fh.in
updates Deville routines, uses subroutines to remove equivalence-statements
updates stations and source in CPML acoustic examples; out-comments unused array potential_dot_dot_acoustic_old
re-orders loop in Deville routine, leads to faster code on tested systems
updates coupling routines to avoid implicit (hidden) memory copies, fixes #122; updates rule dependencies
updates Par_file in EXAMPLES/meshfem3D_examples/simple_model to match reference solution