swc-windows-installer.py: Generalize update_bash_profile

And rename from make_bash_profile now that we're appending instead of
creating (since af1ec77, Append exports to end of .bash_profile
instead of overwriting, 2013-09-19).

This more general form can be used to add even more paths, for example
our IPython and nosetest entry points.
swc-windows-installer.py: Rework paths in main()

Based on Ethan's path handling in f4e0254e (Add a Nano installer for
Windows, 2013-09-17), while still retaining the entry-point creation
for IPython and nose.
swc-windows-installer.py: De-emphasize Anaconda

Bridge the gap between the original Anaconda plug and Ethan's simpler
"Install Python" from f4e0254e (Add a Nano installer for Windows,
2013-09-17).  As of Anaconda 1.7.0, IPython 1.0.0 and nose 1.3.0 are
included by default [1].

[1]: http://docs.continuum.io/anaconda/pkgs.html
swc-nano-installer.py: Remove now that changes are in swc-windows-installer.py
swc-windows-installer.py: Remove IPython and nose entry points

Ethan thought these had been fixed upstream, and Aron Ahmadia pointed
to the Anaconda v1.6.2 release notes [1]:

  2013-07-09: 1.6.2: (Windows only)

    Fixed path being incorrectly appended on Windows during install

That means we can drop our entry point scripts and fall back to just
installing Nano and setting up EDITOR.

[1]: http://docs.continuum.io/anaconda/changelog.html
swc-windows-installer.py: Rework install paths to use ~/.swc

Instead of cluttering the user's home directory with multiple
SWC-installed directories, reduce clutter and improve namespacing by
dumping everything inside ~/.swc.  Think of it as a SWC-specific
~/.local.  We avoid actually using ~/.local because users might
already be using that for other purposes.

Use os.makedirs to create the nano install directory if it does not
already exist, because ZipFile.extract uses os.mkdir internally, and
mkdir will not recursively create directories.