allow dependencies to use chained methods

[djerius]

See #79

[preaction]

Thanks! Though I've started thinking Beam::Wire is too complicated currently, this seems like a good thing to have. But, could we instead implement it as an array value of $call instead of the array being in $method? Then a single call and multiple calls would look similar:

# Single call w/ args
svc:
    $call:
        $method: init
        $args: []

# Chained w/ args
chain:
    $ref: ...
    $call:
        - $method: init
          $args: []
        - $method: attr
          $args: ['value']

# Single call w/o args
svc:
    $ref: ...
    $call: init

# Chained w/o args
chain:
    $ref: ...
    $call:
        - init
        - and_again

I don't think this is really useful without method chaining, so we can probably just assume it's chaining (otherwise, I suspect, one would just call the methods in code).

I can make that change if you'd like, or you can and I can merge it.