NDBuffer: Move out of the hdf5 subdirectory
Move data_type_to_size from DataTypeHDF5 to DataType

We therefore don't have to include HDF5 specific DataTypeHDF5
in NDBuffer anymore
[test] reactive tests for NDBuffer after adapting them for nix
Rename: NDBuffer -> NDArray
DataType: Add [u]int8 support for to_data_type
NDSize: add a description to a exception

Still need a better exception though
[test] Add NDArray IO test to DataSet
DataType: explicitly import stdexcept

This should fix the build for gcc. Ups.
Merge pull request #43 from gicmo/ndbuffer

Reactivate NDBuffer as NDArray
Unit test for nix::File
Remove old unit tests for File from tmp directory
Merge pull request #44 from stoewer/master

New unit test for nix::File

Tested locally. All fine.