Fix broken link error in CI

pulldown-cmark's link checker does not recognize <span> apparently.
We therefore have to rely on markdown footnotes instead.
As those footnotes use labels like 1 or 2, those could easily be confused
with counts. Thus we hide those and use non-numeric labels.

Author: est31

src/statements.md

@@ -54,11 +54,11 @@ fn outer() {
 > **<sup>Syntax</sup>**\
 > _LetStatement_ :\
 > &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> `let` [_PatternNoTopAlt_]
->     ( `:` [_Type_] )<sup>?</sup> (`=` [_Expression_][†](#let-else-restriction)
+>     ( `:` [_Type_] )<sup>?</sup> (`=` [_Expression_] <sup>[†](#let-else-restriction)</sup>
 >     ( `else` [_BlockExpression_]) <sup>?</sup> ) <sup>?</sup> `;`
 
-<span id="let-else-restriction">† When an `else` block is specified, the
-_Expression_ must not be a [_LazyBooleanExpression_], or end with a `}`.</span>
+[^let-else-restriction]:<sup>†</sup> When an `else` block is specified, the
+_Expression_ must not be a [_LazyBooleanExpression_], or end with a `}`.
 
 A *`let` statement* introduces a new set of [variables], given by a [pattern].
 The pattern is followed optionally by a type annotation and then either ends,

theme/reference.css

@@ -51,3 +51,11 @@ main .warning p::before {
 .ayu main .warning p a {
     color: #80d0d0;
 }
+
+/*
+We want to use our own footnote labels such as †.
+For this, we have to hide the builtin ones.
+*/
+.footnote-definition-label {
+    display: none;
+}