Make VecList a GADT and expose its consturctors

It becomes type safe then
Remove unneeded constraint from changeMonad
There's no point in hiding constructor of ContVecT
Add highly inefficient implementations of sequenceA and
traverse for vectors
Add Traversable instance for VecList
Typeable instance for VecList
Add missing instances to boxed vectors
Add missing Typeable instances
More missing instances
Type synonims for 4 and 5 element vectors
Add changelog