Write git revision into output file

 - Was not working since transition to github
PyAxi: Adapt to new reference files

* Reference traces start at t=0s, too.
* Removes workaround from b5d270c74aaab1fe654a391e1944febef04a66bc
Python script to start nightly tests

 - These tests are stored in repository sstaehler/axisem_nightly_testing
Introduce tests 18-20 (gfortran)
Merge branch 'master' of https://github.com/geodynamics/axisem
Add preprocessor flag include_mpi

 - Allows to use MPI by "include mpif.h" instead of "use mpi".
 - Kind of a hack, but otherwise running the code is not possible on machines with more than one version of gfortran installed. Also applies to other compilers sometimes, when openmpi was not compiled with exactly the same version
makemake.pl ignores include in .f90 files

 - To avoid an entry for mpif.h
 - In case somebody wants to use a 'include' in this Fortran2003 code, please mail me
Merge branch 'master' of https://github.com/geodynamics/axisem into HEAD

Conflicts:
	SOLVER/Makefile.TEMPLATE
should be identical in mesher and solver
Merge branch 'master' of https://github.com/geodynamics/axisem
background_models.f90 is now linked and not copied anymore
link instead of duplicate files
unifiying analytic_semi_mapping
unfiying subpar_mapping.f90 in mesher and solver
removing unused module
adapting to axisem style
finishing styling
removing splib from solver

gll points and lagrange derivatives now computed in mesher and stored to the mesh
tidy up
fixing a typo