make interval gls entry

rules/interval.tex

-The day has four intervals:
+The day has four \glspl{interval}:
 
 \noindent
-\begin{tabularx}{\linewidth}{Y|c|c|Y}
+\begin{tabularx}{\linewidth}{c|c|c|Y}
 
   \hline
   1 \textbf{Morning} & 2 \textbf{Afternoon} & 3 \textbf{Evening} & 4 \textbf{Night} \\
@@ -9,13 +9,13 @@ The day has four intervals:
 \end{tabularx}
 \vspace{.3em}
 
-At the end of each Interval, a number of things happen:
+At the end of each \gls{interval}, a number of things happen:
 
 \begin{itemize}
   \item
-  The \gls{gm} rolls 1D6, and every character who took part in the Interval regenerates that many \glspl{fp}.
+  The \gls{gm} rolls 1D6, and every character who took part in the \gls{interval} regenerates that many \glspl{fp}.
   \item
-  Characters who rested for the Interval regenerate a number of \glspl{ep} equal to half their current \glspl{hp} (round up).
+  Characters who rested for the \gls{interval} regenerate a number of \glspl{ep} equal to half their current \glspl{hp} (round up).
   \item
   The \gls{gm} divides a number of \glspl{mp} between everything in the area which can hold \glspl{mp} (round up).
   \begin{itemize}