Merge travis cleanup

- platform specific constraints fixed via Makefile variables
- cabal constraints are given on the command line.
- Packages are built from the tarballs directly

This means that all the cabal config changes are no more required.
Fixed some of the documentations in raaz-cipher
removed unwanted imports
renamed Buffer to MemoryBuf
use System.Process instead of depreciated System.Cmd
raaz-random fixed to use MemoryBuf instead of Buffer
some more import cleanup
removed local-rep-clean target from clean
documentation of Raaz.Hash improved
toHex and toBytestring exposed by individual hash modules

If one is interested only in a particular hash then they can use the
corresponding module with all the interfaces avaliable.
stop hlint bitching about import/export shortcut
Added writeByteString
Added testPokePeek
hlint cleanup
refactored the padLength and shaPadding
changed sha hashes to use refactored padLength and padding
refactored sha1 trans function
Merge cleanup raaz-hash

- hlint fixups and associated refactoring
- refactoring padLength and padding of sha hash family
criterion version drops