Inconsistent argument naming for directory_url and server_url

[kellpossible]

• It's referred to as directory_url here:
  • https://docs.rs/instant-acme/latest/instant_acme/struct.Account.html#method.from_parts
• It's referred to as server_url here:
  • https://docs.rs/instant-acme/latest/instant_acme/struct.Account.html#method.create
  • https://docs.rs/instant-acme/latest/instant_acme/struct.Account.html#method.create_with_http

It would be good for this to be more consistent, or descriptive. It looks like server_urls in any case is used in Client to perform a request and fetch the directory, so perhaps directory_url is a better name.

See also #50 (comment)

[kellpossible]

Other ACME implementations also make it obvious that this URL is related to the directory concept:

• https://docs.rs/instant-acme/latest/instant_acme/struct.Account.html#method.create
• https://docs.rs/async-acme/latest/async_acme/acme/struct.Directory.html#method.discover
• https://docs.rs/acme-client/latest/acme_client/struct.Directory.html#method.from_url

[djc]

I think renaming this to directory_url everywhere probably makes sense, want to send a PR to do that?

[kellpossible]

Sure thing! Happy to do that now

[kellpossible]

Okay I've created a branch off #50 over at https://github.com/kellpossible/instant-acme/tree/directory-url-argument-rename which I'll rebase and submit as an MR once #50 is merged to save on any merge conflict resolution that may be necessary.