interledger-btp API review for v1.0-rc

[gakonst]

interledger-btp public items marked with x are documented. Non-exported items are not taken into account. Follows format from #561.

Part of #557.

• BtpAccount (trait)
  • Should the trait functions also be documented? Seem a bit self explanatory from the name
• BtpStore (trait)
• connect_client (fn)
• connect_to_service_account (fn)
• parse_btp_url (fn)
  • Should this be removed? We do not use it anywhere, and just manually remove the btp+ prefix here: https://github.com/interledger-rs/interledger-rs/blob/master/crates/interledger-btp/src/client.rs#L63
• btp_service_as_filter (fn)
  • This is documented, but the comment is outdated. Needs to be updated to show that it converts the provided btp service to a warp filter
• BtpOutgoingService (struct)
• BtpService (struct)

[bstrie]

• parse_btp_url: remove it if we can get away with it

[gakonst]

Yup it's been removed