Remove PyReadline as an install requirement on Windows

How about removing pyreadline as an install requirement on Windows for version 2.0 so IPython can be used without pyreadline? 

AFAIK the current situation is:

* IPython can be installed without pyreadline using bdist_wininst installers.

* The IPython scripts in sys.prefix\Scripts do not work if pyreadline is not installed (fixed by this PR).

* The IPython console can be used without pyreadline, in which case a warning is printed that "Proper color support under MS Windows requires the pyreadline library".

* Pyreadline is not used/required by the IPython Qt console and the notebook.

* Pyreadline 2.0 conflicts/interferes with the colorama package and pip usage: See <https://github.com/pypa/pip/issues/1314> and <https://github.com/pyreadline/pyreadline/issues/18>

* Pyreadline changes the tab key behavior on the standard Windows console. See <http://stackoverflow.com/questions/20353511/python-command-line-not-accepting-tabs>

* The Pyreadline project seems abandoned (the last commit was a year ago)