[macros] Create \tref and \fref commands if they doesn't exist yet.

The existence of \tref and \fref seems to have changed as package
versions have been evolving.

Author: tkoeppe

source/macros.tex

@@ -406,8 +406,10 @@
 \ExplSyntaxOff
 
 %% Inline non-parenthesized table reference (override memoir's \tref)
+\providecommand{\tref}{}
 \renewcommand{\tref}[1]{\hyperref[tab:#1]{\tablerefname \nolinebreak[3] \ref*{tab:#1}}}
 %% Inline non-parenthesized figure reference (override memoir's \fref)
+\providecommand{\fref}{}
 \renewcommand{\fref}[1]{\hyperref[fig:#1]{\figurerefname \nolinebreak[3] \ref*{fig:#1}}}
 
 %% NTBS, etc.