Finalise documentation for Milestone 1.0, including in the JOSS paper

[bnlawrence]

• Need to make sure that Proposal for is_cloud_optimized #145 is documented and included.

• Need to make sure the JOSS paper includes anything we've added since we wrote the first draft.

[bnlawrence]

Ok, I think the current joss paper covers the key points now, and so we don't need to keep this issue open