Discourse users and associated accounts are created or updated when a
user logins or connects the account using their account preferences.
This new API can be used to create associated accounts and users too,
if necessary.
Documenting the `/u/:username:/emails.json` endpoint.
Also removing some email fields from user api responses because they
aren't actually included in the response unless you are querying
yourself.
`nullable` is no longer a valid type, and types also can't be an empty
string, so just bringing a number of issues with types in compliance
with the openapi spec.
* document user endpoints, allow for empty request/response bodies
* document more user endpoints, improve debugging output if no details are specified
* document some more user endpoints
* minor cleanup
* FIX: flakey tests due to bad regex
