Add notation for `div`

This commit add notation for `div`: we use unicode 'division sign'. The
notation complies with base-unicode-symbols[1].

[1] http://hackage.haskell.org/package/base-unicode-symbols
Add some more set notation

The new notation is in accordance with

  http://hackage.haskell.org/package/base-unicode-symbols
Add notation for boolean operations

The new notation is in accordance with

  http://hackage.haskell.org/package/base-unicode-symbols
Merge pull request #10 from enomsg/for-upstream

Respin of some additions: div, set and boolean notation