Basic keyboard accessibility CSS tweaks

Mostly doubling-up :hover styles to also cover :focus, as a first step
to making the framework more keyboard-friendly.
Additionally, fixed two small markup issues in the docs/examples to
make the "Learn more" large primary button-styled links
keyboard-focusable (as without href they're treated as non-tabable
anchors).

less/pager.less

@@ -20,7 +20,8 @@
   border: 1px solid #ddd;
   .border-radius(15px);
 }
-.pager li > a:hover {
+.pager li > a:hover,
+.pager li > a:focus {
   text-decoration: none;
   background-color: #f5f5f5;
 }
@@ -34,6 +35,7 @@
 }
 .pager .disabled > a,
 .pager .disabled > a:hover,
+.pager .disabled > a:focus,
 .pager .disabled > span {
   color: @grayLight;
   background-color: #fff;