Progress: Heart font, from Font Squirrel

The current fonts don't have a ♡ glyph, which makes it look different in
different browsers and on different OSes.

DejaVu Serif does contain the glyph. Here's a profile of it that contains
just that character and ♥, exactly as downloaded from Font Squirrel.
Enhancement: Consistent file names

Match the rest of the project.
Prefactoring: class=heart, not class=red

Be specific about the reason for being red, for forthcoming font
substitution change.

(Sorry, diamonds.)
Enhancement: Consistent heart font

Specify a heart font that's known to have the ♡ and ♥ glyphs in it, so
they look consistent across platforms, and can be sized appropriately.