don't add `-e` requirements in setup.py

They don't work properly, so don't try.
This means that until IPython 3 is released,
`pip install -e .` will be insufficient.
IPython will need to be installed separately.
install requirements explicitly in README

needed for IPython from dev
Don't install requirements in Dockerfile

`pip install .` covers that

The one exception is IPython master,
which is inherited from the base image.
Merge pull request #93 from minrk/setup-no-e

don't include `-e` requirements in setup.py