Adding character stats section.

This code isn't perfect, there's definitely some room for DRY. I plan
to fix a few things:

1. Helper functions (`p`, `pr`, `pct`) are duplicated in multiple
   files. These should be combined into a utility library or an actual
   domain model.
2. There should probably be a domain model that calculates the values
   instead of throwing everything into the `calcSheetDamage` and
   `render` functions of the `Page` component.
3. I still don't fully understand when to use state vs. props but I
   am working to move most of the state into the `Page` component to
   have that push the data to the sub-components via props.

There is also the matter of the `%root%` placeholder. I need to make
some kind of environment configuration so that making a distribution
for GitHub vs. my local server becomes easier.