Now it is possible to specify WOLFE_C1_SL and WOLFE_C2_SL in the JSON input file.
Documentation is updated as well.
Smaller output improvements.

Fixed a bug which prevented to stop at max FC when FC_END was not a multiple of FC_INCR.
Additionally L-BFGS will try step length 1 first every time a new frequency stage is choosen.

Added the option WRITE_FILTERED_DATA to write time filtered measured data to disk.
If WRITE_FILTERED_DATA is not set in the JSON file, it will be set to 0.

Added debugging output for VP and renamed some variables to be consistent within the code.

Removed all checkpointing things in the code.

Removed TIME_FILT==1 from SH toy example

Removed the option HESSIAN from the code.

Workflow file now includes a header.

Updated documentation to include all new variables which are available in the JSON input file.

Update: Merge test

-Remove src_relicts
-Clean up of the Makefile in src/

Removed gfortran and f2c as known dependency.

adjustment of acoustic toy-example, scaling of the elastic explosive source and acoustic free surface condition.

Code in contrib/aff/tests is not required as part of Seitosh.
However, the test code requires additional settings like proper interlanguage
linking (C++ and Fortran). To reduce the constraints on the installation
environment, discard the subdirectory tests in contrib/aff entirely, as well
as all references to the test code made in the Makefile.

Programs in contrib/stfinv/tests are not required by DENISE but may cause
confusion since they require libtfxx which is not part of the vendor import.

The Fortran part of the vendor code is not used by DENISE. It can safely be
discarded. This way, no Fortran compiler is required when compiling and
installing the code in subdirectory contrib, except for code in aff/tests,
which however is not part of the install target.

Check whether FC is set from the value of implicit variables (origin is
default). If yes, replace value of variable. If not, FC most likely is set by
intention of the user. Do not alter the value in this case.

Let doxygen output be written to a subdirectory of contrib rather than
$(HOME)/public_html

To make the doxyview target operational an absolute path name is required.
Therefore add the abspath function of make to the generation of variable
CONTRIBDIR.

Since vendor Makefiles make use of special GNU make features, we can safely
rely on GNU make being in operation. GNU make provides the variable
MAKEFILE_LIST from which the relative path can be extracted at which
Makefile_var was found. This exactly is the path of the contrib directory,
such that the user (calling Makefile) needs not set this variable.

Currently the calling Makefiles still set a variable CONTRIBDIR which then
simply is overwritten in Makefile_var. Such the setting of CONTRIBDIR is
unnecessarily doubled.