Implement Users - Githubissues

[ ] pinned-users (use User().Pinned() or something similar to fit in the service properly)
[ ] username/available (same)
[ ] users (there is no List endpoint on users, so we can use it for that)
[ ] users/followers
[ ] users/following
[ ] users/get-frequently-replied-users
[ ] users/notes
[ ] users/recommendation
[ ] users/relation
[ ] users/report-abuse
[ ] users/search-by-username-and-host
[ ] users/search
[ ] users/show

yitsushi / go-misskey