Fixed type checking of undefined
Cleaned cleantt even more
Added eta expansion for constructors
Merge branch 'minitt' of https://github.com/simhu/cubical.git into minitt
Add several universes, plus constructor and subtyping rule
Example file to test typing with plus
One example with sigma types
Merge branch 'minittplus' of https://github.com/simhu/cubical.git into minittplus