Use nyan file version number for parsing

[TheJJ]

In order to prevent compatibility problems in the future, we should require a nyan version number in each nyan file.

Proposal:

# blabla copyright whatnot
# then the version specification
!format nyan 1.0

# blablabla
Object():
   ...

[TheJJ]

Basic support landed with #87, but we don't verify it yet or parse the file depending on the fie.