Add Erlang support

The standard Erlang style is to indent code inside a block relative to
the token that opens the block.  For example:

    bar(X) ->
      {A, B} = case X of
                 true ->
                   {alpha, [beta,
                            gamma]}
               end.

Thus it is best to ignore the code inside these block constructs when
determining the indent offset.
Merge pull request #9 from dhull/erlang

Add Erlang support