[operators] use csc_matrix instead of csr_matrix

otherwise, spilu will complain an make a copy.
[operators] add more invert_options for NumpyMatrixOperator

and add a default to choose which is the default sparse solver
[core.cache] add username to cache filename for dogpile backends
[parameters.base] cleanup
[docs] update/add documentation
[docs] add/update documentation
[docs] do note document private module functions without docstring
[docs] bugfix
[docs] better handling of builtins
[docs] prevent sphinx from documenting __weakref__
[docs] update/add documentation
[docs] also blacklist __init__
[docs] add __setitem__ to Mock class for readthedocs
[docs] add getting started document
[docs] fix typos
reanme PYMOR_DONT_COPY_DOCSTRINGS to PYMOR_COPY_DOCSTRINGS_DISABLE
[docs] remove separate contents.rst
[docs] improve sorting in module index
[docs] document environment variables
[docs] update index.rst