Make branchAll() and renderAll() on non-iterable types consistent with branch() and render()

• Make branchAll() and renderAll() on non-iterable types consistent with branch() and render()
  • No longer throw errors if branchAll() or renderAll() is called on a non-iterable form, instead returning an empty array.
• Make returned forms from non-branchable types read-only
• Fix docs that were incorrect at describing intended behaviour of branch() and render()
• Define expected behaviour of branchAll() and renderAll(). As this was previously undefined behaviour according to the API this is regarded as a non-breaking change - and at this early stage its a very reasonable bet that nobody is relying on catching error messages from branchAll() and renderAll() for their apps to function

No breaking changes (if you aren't relying on the previously undocumented behaviour of requiring branchAll() and renderAll() throwing errors when called on non-iterable forms)