non-blocking glue in IPython notebook
Removed uniqueness constraint on data labels

As far as I can tell, this constraint has no logical impact on Glue.
User's will disambiguate labels themselves in most cases, and
the disambiguation is awkward when multiple Glue sessions are called
per python process
PEP8
doc tweak
Merge pull request #162 from ChrisBeaumont/ipy

Better IPython notebook integration