gmiflink – Simplify usage of \hypertarget and \hyperlink

Three hy­per­ref-based macros that sim­plify us­age of \hy­per­tar­get and \hy­per­link: one ar­gu­ment in­stead of the same one twice. Also \gmi­flink and \gmifref which type­set plain text in­stead of gen­er­at­ing an er­ror or print­ing ‘??’ if there is no re­spec­tive hy­per­tar­get or la­bel.