Merge back to a single package

One of the main reasons for moving into a backpack based interface was
to allow advanced users, who know about their hardware, to plugin
appropriate implementations seamlessly into their cryptographic
library. The cabal interface only allowed one public component to be
exposed from a package and backpack needs ability to separate
signatures and modules that use signatures into different component to
avoid recursion. Thus the only solution was to split the raaz library
into multiple packages. This had the following downside

1. Each package requires their own .cabal file and hence one cannot
   use the common section across all these very similar package

2. Unnecessary pollution of the package name space.

Besides this and other reasons, cabal-install is now being modified to
support multiple public components from the same package. In
anticipation, we merge all the packages back to a single package.

Reference

1. The original issue is described at <haskell/cabal#4206>
2. The GSoC work is available at <haskell/cabal#5526>