Use / (or s) to open search box

We allow for using `s` to open the search box, but it's more common to
use `/` (forward slash) for this.  E.g., MDN's documentation uses `/`
for search.  Rustdoc and GitHub accept either.

Let's allow either key to be used, and let's switch to "advertising"
`/` rather than `s` in the hover text for the search button.

In making that switch, let's also simplify that hover text a bit.
Previously it had said "Search. (Shortkey: s)".  This was the only top
button on which we had included a period in the hover text.  Let's
remove that, and let's remove the "shortkey" bit of jargon.  It's
enough to just put `/` in a parenthetical, i.e. "Search (`/`)".
People will gleam from that what we mean.

We've also updated the guide accordingly.

Author: traviscross

guide/src/guide/reading.md

@@ -42,7 +42,7 @@ Tapping the menu bar will scroll the page to the top.
 ## Search
 
 Each book has a built-in search system.
-Pressing the search icon (<i class="fa fa-search"></i>) in the menu bar, or pressing the `S` key on the keyboard will open an input box for entering search terms.
+Pressing the search icon (<i class="fa fa-search"></i>) in the menu bar, or pressing the `/` or `S` key on the keyboard will open an input box for entering search terms.
 Typing some terms will show matching chapters and sections in real time.
 
 Clicking any of the results will jump to that section.

src/front-end/searcher/searcher.js

@@ -35,7 +35,7 @@ window.search = window.search || {};
         URL_SEARCH_PARAM = 'search',
         URL_MARK_PARAM = 'highlight',
 
-        SEARCH_HOTKEY_KEYCODE = 83,
+        SEARCH_HOTKEY_KEYCODES = [83, 191], // `s` or `/`.
         ESCAPE_KEYCODE = 27,
         DOWN_KEYCODE = 40,
         UP_KEYCODE = 38,
@@ -362,7 +362,7 @@ window.search = window.search || {};
             }
             showSearch(false);
             marker.unmark();
-        } else if (!hasFocus() && e.keyCode === SEARCH_HOTKEY_KEYCODE) {
+        } else if (!hasFocus() && SEARCH_HOTKEY_KEYCODES.includes(e.keyCode)) {
             e.preventDefault();
             showSearch(true);
             window.scrollTo(0, 0);

src/front-end/templates/index.hbs

@@ -142,7 +142,7 @@
                             <li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
                         </ul>
                         {{#if search_enabled}}
-                        <button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
+                        <button id="search-toggle" class="icon-button" type="button" title="Search (`/`)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="/ s" aria-controls="searchbar">
                             <i class="fa fa-search"></i>
                         </button>
                         {{/if}}