Fix support for params with arrays of hashes in multipart forms.
Extend the fix from @econsultancy to provide full support for arrays of hashes in multipart.

If we have the following params:
  blah: [{woo: 1, moo: 2}, {woo: 10, moo: 20}]

It would be converted and parsed into:

Before:
  blah: [{woo: 1}, {moo: 2, woo: 10}, {moo: 20}]

Now:
  blah: [{woo: 1, moo: 2}, {woo: 10, {moo: 20}]

Which is obviously what we want.
Provide support for multipart encoding of arrays of hashes that are arbitrarily nested in other arrays and hashes.