Added @see annotation to schemas

Sometimes you only want to write the docs once. I'm looking at you @Vagabond.

Check this schema
```erlang
%% @doc A really long winded description of this configuration value
%% but it also applies to others! I really don't want to type it again
{mapping, "setting.one", "erlang.key", []}.

%% @see setting.one
{mapping, "setting.one", "erlang.key2", []}.
```

Now `./riak config describe setting.two` will display the docs for `setting.one`.

If you have an `@doc` and an `@see` It will print the `@doc` for the setting you're querying, and the `@see` list of other variables to use.

Only one `@see` per line. If you want more than one:

```erlang
%% @see setting.one
%% @see setting.two
```