Create an sketch/archive format

[turicas]

To make sharing sketches easy it would be nice to have an archive format (like a ZIP file) with specific files inside (the sketch code, the compiled code etc.); it'll make some things possible like downloading the sketch archive, sending to somebody so she can upload it using the Web interface.
For this to work we need to specify which files are going into the archive, its names, formats etc. The idea is to make something like Open Document Format (but simpler - not using XML, for example). It'd be cool to have some JSON representation of the archive also, so the sketches will be easily transferred through APIs.