JaggedArray._broadcast should accept scalars and any AwkwardArray

[jpivarski]

Two missing cases. Scalars have an obvious implementation. General AwkwardArrays would turn into JaggedArray(IndexArray(...)).

[jpivarski]

Fixed by #99. Actually, we don't have to introduce IndexedArray; we can use the fact that every awkward array has a fancy indexing implementation to apply the rearrangement eagerly.

Really, the only use of IndexedArray is for lazy rearrangements, the only use of which I can think of is cyclic references.

[jpivarski]

Oh, and dictionary encoding. In case you don't want to eagerly create a huge number of strings from indexes, but only want to lazily describe it.