Add a Nano installer for Windows

1. Downloads and installs Nano into the users home directory
2. Adds Nano to the path
3. Makes Nano the default editor
Switch from using .bashrc to .bash_profile nano path and editor export
Append exports to end of .bash_profile instead of overwriting

In the process at an explanation of where the lines came from
so that users know they can remove the lines if desired.
Remove testing line
Merge branch 'nano-installer' into windows-installer

* nano-installer:
  Remove testing line
  Append exports to end of .bash_profile instead of overwriting
  Switch from using .bashrc to .bash_profile nano path and editor export
  Add a Nano installer for Windows
swc-windows-installer.py: Bring in Ethan's make_bash_profile and make_posix_path

This integerates some of Ethan's nano-installer changes.  In the pull
request, Ethan elaborates on the .bash_profile choice [1]:

  In response to comments on the Tutors list the installer now uses
  .bash_profile instead of .bashrc and appends the lines rather than
  overwriting the file. I have also added comments that indicate where
  the new lines in .bash_profile come from.

  Once the Python version is in I'll move on to getting this compiled
  into a .exe file, which should be more familiar to our students and
  won't run into issues with Canopy installs opening the file in
  Canopy rather than executing it.

The referenced tutors@ discussion is in the messages leading up to
[2], where Ethan top-quotes a discussion with R. David Murray about
the relative merits of .bash_profile and .bashrc.  The imporant point
David made was that .bash_profile is only executed once at login,
while .bashrc is executed for each new shell.  Putting PATH appends in
.bash_profile means that you don't end up adding duplicate entries to
the PATH as you spawn subshells.  For example:

  ${ORIGINAL_PATH}:${NANO_PATH}:${NANO_PATH}:...

[1]: https://github.com/swcarpentry/bc/pull/35
[2]: http://lists.software-carpentry.org/pipermail/tutors_lists.software-carpentry.org/2013-September/000969.html
swc-windows-installer.py: Generalize update_bash_profile

And rename from make_bash_profile now that we're appending instead of
creating (since c5d5414, 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 833d0ee (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 833d0ee (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-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.
swc-nano-installer.py: Remove now that changes are in swc-windows-installer.py