[common.exceptions] marked test_results_missing as deprecated
[test.common_string] add another bool test, refs #12
[common.string] added some meaningfull error messages
[common.configuration] added some meaningful error messages
[test.common_string] added another boolean testcase
[common.string] add specialization of Choose for bool

This adds the possibility to convert 'true' and 'false' together with their
uppercase variants to bool. This allows to use an ini file with dune and
python (as it used to be). Fixes #12
[common.fvector] added another ctor
[common.string] introduce VectorConstructor

This fixes some warnings in 'VectorType vec(size_t)' when VectorType was a
FieldVector< int, ... > bc. of the size_t to int conversion and is a more
general solution in general.
[filesystem] renames ambiguous pathOnly to directoryOnly
[functioninterface] rewire visualize

parallel runs failed if "filename" contains directory parts since
VTKWriter wants to prefix filename with s00000$(RANK)
[common/parallel] adds mpi_abort abstraction
Revert "[functioninterface] rewire visualize"

This reverts commit 9ab7afb6a85a422908ff6fbfa454fc140475c149.
no idea wtf I've commited here...
[functioninterface] _actually_ rewire visualize

parallel runs failed if "filename" contains directory parts since
VTKWriter wants to prefix filename with s00000$(RANK)
[functions] removed from lib completely
[functions.tensor] removed outdated txt from playground
[functions.interfaces] updated visualize()

We fall back to write() in serial runs, avoiding the s0000-p000 prefix
in the output files. Hope this does not break anything, @renemilk?
[test] moved function.hh -> functions.hh
[test.functions] split static create stuff into separate function
[test.functions_flattop] minor update
[test.functions.combined] added test for Difference