Add filter to replace icon font

[vidya-ram]

Currently the following are the html snippet to add
Material icons

<i class="material-icons mui--text-subhead mui--text-light mui--align-middle" aria-hidden="true">perm_identity</i>

And font awesome 5 icons

{% assets "fa5-sprite" %}<svg class="fa5-icon fa5-icon fa5-icon--subhead fa5--align-baseline" aria-hidden="true" role="img"><use xlink:href="{{ ASSET_URL }}#times"></use></svg>{% endassets %}

Instead, {{ micon('icon_name', title='Optional title') }} in the template should insert the full markup for that material icon/font awesome icon including aria-hidden flag.

[vidya-ram]

Fixed in #264 and #265