Add a script to convert SVGs to ICOs

This adds an initial draft of a script which is designed to generate ICO
files such that these icons can be used in Windows programs and other
places that support the ICO format
Icon Generation script

This commit gets the icon generation script making icons that don't look awful.  The initial
draft used convert on the SVG but when used in that mode it resizes awfully.  The new version
using the existing PNGs to generate the icon since the PNGs should be nicely sized.

This also expands the sizes of PNGs generated by the make file to include more sizes that are
typically included in ICO files.

I encountered some slightly weird artifacts in the 128x128 icons but not sure if this is simply
an artifact of the slightly borked ImageMagick install on my OS X box.
Regenerate PNGs and Download Packages

This commit adds the new sizes of PNGs and regenerates the downloads
Fix creation of downloads to include ICO correctly

The previous commit did not correctly include the ICOs in the downloads.  This is now fixed
Improve how readme is generated to use template files which can be easily edited outside the script

This moves the header and main text of the README into separate .md files which are added to
the README generated by update-readme.sh using cat.  This makes it much easier to edit the
text separate from the script.

I also improved the text to discuss how to generate PNGs in different sizes and to cover
the newly added ICO support
Merge pull request #3 from rvesse/master

Add ICO files