This commit improves and changes the templating library in the following ways:
* Templates are now registered/loaded at initialization.
* No synchronization is required to read templates.
* All templates are properly loaded (fixes#122).
* Tera templates are given the proper name: `index`, not `index.html.tera`.
* Rendering tests added for both templating engines.
There is one breaking change:
* Tera templates are given the proper name: `index`, not `index.html.tera`.