Use combinators

--HG--
branch : version-0.5
Add mkN for continuation based vector

--HG--
branch : version-0.5
Doc update

--HG--
branch : version-0.5
Wrap mkN into Fun to allow GHC instantiate types

--HG--
branch : version-0.5
Add mkN for ordinary vectors.

It require explicit type annotations

--HG--
branch : version-0.5