feature(api): an API to upload large in-memory data which returns a datamap address

[happybeing]

I've been looking for ways to upload data other than from disk:

• Data <1MB FilesApi::get_local_payment_and_upload_chunk() will pay for and store a chunk (<~1MB).
  I'm not sure this API is ideal yet for external use as I didn't see validation of the data size being done.

• Data >1MB I'm not aware of an API that will store data larger than a Chunk (other than from a file).

Missing APIs
I believe there's a need new APIs that encrypt and upload in-memory data which is too large for a chunk. For example, equivalents of the following for a block of data rather than a file or file-tree:

FilesUploader
start_upload()
ChunkManager
chunk_file()
encrypt_large()

This is not a simple thing to do effectively, so without this developers will probably write data to a file and upload that which is not secure and risks leaking private information.