Update the h5 interface

I have updated the h5 interface and added/removed some tests (they also tested basic h5 functionality which is already done in h5).

added doxygen documentation (I would have done it anyway in the docs PR)
cleaned up includes
removed some unnecessary copies (when writing/reading into views which are not contiguous in memory)
removed some unnecessary restrictions, e.g. allow to read into a view on an nda::array<std::string,...> or into a view with a non-C memory layout, ...
cleaned up the tests

TRIQS / nda