backwards compat for font awesome 3.0 for fonts sphinx_rtd was using.

fixes #95

sass/_theme_font_awesome_compatability.sass

@@ -0,0 +1,20 @@
+.icon
+  @extend .fa
+.icon-home
+  @extend .fa-home
+.icon-search
+  @extend .fa-search
+.icon-book
+  @extend .fa-book
+.icon-caret-down
+  @extend .fa-caret-down
+.icon-github
+  @extend .fa-github
+.icon-bitbucket
+  @extend .fa-bitbucket
+.icon-fire
+  @extend .fa-fire
+.icon-circle-arrow-right
+  @extend .fa-arrow-circle-right
+.icon-circle-arrow-left
+  @extend .fa-arrow-circle-left

sass/theme.sass

@@ -53,3 +53,4 @@
 @import theme_badge
 @import theme_rst
 @import theme_mathjax
+@import theme_font_awesome_compatability

sphinx_rtd_theme/footer.html

@@ -2,10 +2,10 @@
   {% if next or prev %}
     <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation">
       {% if next %}
-        <a href="{{ next.link|e }}" class="btn btn-neutral float-right" title="{{ next.title|striptags|e }}"/>Next <span class="fa fa-circle-arrow-right"></span></a>
+        <a href="{{ next.link|e }}" class="btn btn-neutral float-right" title="{{ next.title|striptags|e }}"/>Next <span class="fa fa-arrow-circle-right"></span></a>
       {% endif %}
       {% if prev %}
-        <a href="{{ prev.link|e }}" class="btn btn-neutral" title="{{ prev.title|striptags|e }}"><span class="fa fa-circle-arrow-left"></span> Previous</a>
+        <a href="{{ prev.link|e }}" class="btn btn-neutral" title="{{ prev.title|striptags|e }}"><span class="fa fa-arrow-circle-left"></span> Previous</a>
       {% endif %}
     </div>
   {% endif %}