Fix completion with ipython/ipdb

Lookup special attributes `_getAttributeNames` and `trait_names` via
`super()`.
added delete method
Merge pull request #5 from blueyed/doc-fixes

Minor doc fixes/typos
Merge pull request #3 from blueyed/fix-ipython-completion

Fix completion with ipython/ipdb
Update README.md
Update README.md
minor: doc: punctuation/typos
doc: rephrase intro/desc about zipa: more concice and to the point