PEP8
Remove unused code
Small improvements to _NoDeadNodes and NodeCache.

Now they behave a little bit more like a dict.
Formatting
New node manager
Remove the old machinery in favour of the NodeManager
Use NodeManager.flush_nodes
Use the new NodeManager.close_subtree and NodeManager.shutdown methoods
Update dic regarding NODE_CAHCE_SLOTS
Re-introduce the old DictCache bechavior
Typo fix and rewording (thanks to Francesc)
Revert chances in NODE_CACHE_SLOTS doc.

The possibility to use a DictCache has been re-introduced in 310b355.
Blosc updated to v1.3.1
Merge branch 'issue306' into develop
Catch ClosedNodeError in tables.file.NodeManager._close_nodes
Add links to node reference doc in the FAQ (closes: gh-321)
PEP8