first stab at POSIX-style softlinks
fixed is_dangling() test
allow underscores but explicitly look for  prefixes in attribute names (to make  etc. work on target nodes)
__getitem__, __setitem__, __str__, copy, move, remove, rename all tested and working for Array and Table targets. TODO: tab autocompletion from target node's attributes?
test case for get/set target node attributes via softlink
fixed for case where softlink-->group.child.attribute ('Group' object has no attribute '<name>')
added test cases for softlink-->group.child.attribute and softlink-->softlink-->group.child.attribute
initial working version of ptree, walk_nodes is a bit slow
Disable test on unicode filenames on windows (see gh-389).

Unable to fix issue gh-389 due to lack of access to a build environment
on windows.
Anyway no user reported the problem until a specific test has been enabled
in the test suite so I assume the issue is not blocking for the vast majority
of the users.
Skip tests on comression libs that are not available
improved 2-pass method, can now get node/branch size as % of total. I have some doubts about whether this will work properly for all types of unbalanced tree, though...
I think it will now correctly visit each node only once, without having to store the number of visits in a separate dict
sorting nodes by name, size, natural order
Merge branch 'tmp' into pttree
print details of arrays/tables if they fall at exactly max depth
catch NotImplementedError raised on <VLArray>.size_on_disk and warn instead
Merge branch 'enhanced_softlinks' into develop
Update reease notes (closes: gh-399)
Fix sphinx warnings
Update sphinx conf.py and sphinx build makefiles