Fix some minor mistakes

List exposed-modules alphabetically. Add OverloadedStrings to
other-extensions.

put 'propDeserialiseList' into the 'testGroup'.

Import Data.ByteString.Lazy as LB, not BL.

Deduplicate data constructor in 'signMessage'.

Signed-off-by: Stian Ellingsen    <stian@plaimi.net>
Reviewed-by:   Alexander Berntsen <alexander@plaimi.net>
Signed-off-by: Alexander Berntsen <alexander@plaimi.net>
Perform some cosmetic cleanup

Prefer typing a few chars extra rather than the mental overhead of a
bunch of new variables via 'where's.

Make 'splitMut', 'mutateMut', 'insMut' & 'delMut' top level declarations
with docstrings. This reduces the mental overhead of a bajillion wheres
in the same function, makes the morphisms obvious and is just nicer in
general.

Add missing Haddock string for 'newMutable'.

Use liftA instead of bind.

Use an enum instead of a huge string literal.

Fix some whitespace and alignment errors.

Signed-off-by: Alexander Berntsen <alexander@plaimi.net>
Signed-off-by: Stian Ellingsen <stian@plaimi.net>
Reviewed-by: Stian Ellingsen <stian@plaimi.net>