Use a bold question mark rather than the dingbat char

in the navigation icons. To avoid it getting rendered as a colored emoji
on platforms that don't have text emoji fonts.

Author: marijnh

src/chapter.html

@@ -16,7 +16,7 @@
   <<if $in.prev_link>><a href="<<t $in.prev_link>>.html" title="previous chapter" aria-label="previous chapter">◂</a> <</if>>
   <a href="index.html" title="cover" aria-label="cover">●</a>
   <<if $in.next_link>> <a href="<<t $in.next_link>>.html" title="next chapter" aria-label="next chapter">▸</a><</if>>
-  &nbsp;<button class=help title="help" aria-label="help">❓&#xFE0E;</button>
+  &nbsp;<button class=help title="help" aria-label="help"><strong>?</strong></button>
 </nav>
 
 <h1<<if $in.id>> id="<<t $in.id>>"<</if>>><<if $in.chap_num>><span class=chap_num>Chapter <<t $in.chap_num>></span><</if>><<t $in.title>></h1>
@@ -27,7 +27,7 @@
   <<if $in.prev_link>><a href="<<t $in.prev_link>>.html" title="previous chapter" aria-label="previous chapter">◂</a> <</if>>
   <a href="index.html" title="cover" aria-label="cover">●</a>
   <<if $in.next_link>> <a href="<<t $in.next_link>>.html" title="next chapter" aria-label="next chapter">▸</a><</if>>
-  &nbsp;<button class=help title="help" aria-label="help">❓&#xFE0E;</button>
+  &nbsp;<button class=help title="help" aria-label="help"><strong>?</strong></button>
 </nav>
 </article>