mpwt 0.5.9

[ArnaudBelcour]

Add:

• __version__ in mpwt init file to handle version (issue #59).

Fix:

• error when creating dat files without input folder (issue #61).

Modify:

• refactor how paths are handled (issue #60). This is a first step to the compatibility of mpwt on Windows. But this will need more tests and modification.