change the :set directive to behave like ghci.

What used to be :set is now :option.

Addresses (#108 part 1), if you use :set -XExistentialQuantification

The -package flag is broken for now.
remove unneeded import
add Monoid Display instance
depend on aeson < 0.7 due to ByteString instances removed in that version
Merge pull request #124 from aavogt/set_dynflags

:set behaves like in ghci
Merge branch 'master' of https://github.com/gibiansky/IHaskell