[enh] display helpers in .help()
[doc] add docstrings to ImportNode helpers
[doc] documents helpers shown in .help()
[doc] suggestion of pull request for more helpers
[mod] don't use RedBaron where it doesn't belong
[doc] update installation info
[doc] modify prerequisites of tutorial
[enh] test for copy()
[enh] test dumps()
[enh] test .fst()
[enh] weak test on .help()
[enh] some tests on magic assign
[enh] add test on assign for nodelist
[enh] add .parent to node and nodelist (with testing now \o/)
[doc] document .parent
[fix] correctly set .parent on assign
[doc] inform that RedBaron will take care of setting .parent on assign
[enh] save on which attribute a node is set on the parent
[doc] inform of the existance of .on_attribute and that it's also correctly set on assign
[enh] add tests for _get_helpers