Make h1-h3 css overridable through .de statements

Hi Roger,

I think this would be an improvement on how the CSS related to h1-h3 elements is done.

The way that h1-h3 statements are currently generated do not allow for users to easily override the CSS styles text-align, font-weight or font-size. This change allows users customize these values using a .de directive.

.de h1 { font-weight: bold; font-size: 2.0em; }

What this change does is instead of placing the standard settings (the inital value of hcss) into the .c00x class it uses the h1 element selector to define them.