[feature] custom links for pro users

[CodeMyst]

Pro version, users can use custom links like https://paste.myst.rs/X/compiler_error, X is either the username or the permalink set by and for the user. compiler_error is the custom link. So like if I wanted to paste my compiler error into a paste, it would be like https://paste.myst.rs/anf/compiler_error, remember that my pastemyst username is ANF-Studios.