Update web font to Atkinson Hyperlegible (#938)

Use [Atkinson Hyperlegible Font](https://brailleinstitute.org/freefont)
instead of Open Sans so that letters like i and l can be differentiated.
Fonts are served using Web Open Font Format 2 (woff2) format.
Also set body and paragraph font-size to 1.05em, and set standard
font-weight values.

Author: weiji14

doc/_static/fonts/Atkinson-Hyperlegible-Bold-102a.woff2

@@ -3,18 +3,23 @@ html {
 }
 
 body {
-    font-family: 'Open Sans', sans-serif;
+    font-family: "Atkinson Hyperlegible", sans-serif;
+    font-size: 1.05em;
 }
 
 h1, h2, h3, h4 {
-    font-weight: 300;
-    font-family: "Open Sans",sans-serif;
+    font-weight: normal;
+    font-family: "Atkinson Hyperlegible", sans-serif;
 }
 
 h1 {
     font-size: 200%;
 }
 
+p {
+    font-size: 1.05em;
+}
+
 .gmtplot-output {
     width: 100%;
     overflow: auto;
@@ -131,3 +136,34 @@ a.copybtn {
     user-select: none;
 }
 
+/* Atkinson Hyperlegible regular */
+@font-face {
+    font-family: "Atkinson Hyperlegible";
+    src: url("./fonts/Atkinson-Hyperlegible-Regular-102a.woff2") format('woff2');
+    font-weight: normal;
+    font-style: normal;
+}
+
+/* Atkinson Hyperlegible bold */
+@font-face {
+    font-family: "Atkinson Hyperlegible";
+    src: url("./fonts/Atkinson-Hyperlegible-Bold-102a.woff2") format('woff2');
+    font-weight: bold;
+    font-style: normal;
+}
+
+/* Atkinson Hyperlegible italic */
+@font-face {
+    font-family: "Atkinson Hyperlegible";
+    src: url("./fonts/Atkinson-Hyperlegible-Italic-102a.woff2") format('woff2');
+    font-weight: normal;
+    font-style: italic;
+}
+
+/* Atkinson Hyperlegible bold italic */
+@font-face {
+    font-family: "Atkinson Hyperlegible";
+    src: url("./fonts/Atkinson-Hyperlegible-BoldItalic-102a.woff2") format('woff2');
+    font-weight: bold;
+    font-style: italic;
+}