Add fa-content() function from #139

src/doc/assets/fork-awesome/scss/icons.scss.txt

@@ -4,4 +4,4 @@
    readers do not read off random characters that represent icons */
 {% for icon in icons %}{% for alias in icon.aliases %}
 .#{$fa-css-prefix}-{{ alias }}:before,{% endfor %}
-.#{$fa-css-prefix}-{{ icon.id }}:before { content: $fa-var-{{ icon.id }}; }{% endfor %}
+.#{$fa-css-prefix}-{{ icon.id }}:before { content: fa-content($fa-var-{{ icon.id }}); }{% endfor %}