Cleaning up directory structure for github

[ryzhyk]

• Compress history where necessary
• flatten the spec directory (no "darpa" stuff)
• apps/ -> tools/
• tsl2 -> termite
• test -> ????
• add synthesis competition solver

[adamwalker]

Done, except syntcomp solver. Does that really belong here?

[ryzhyk]

I don't think that it belongs. For some reason I thought you wanted it there.