[Nitro] [OG] eval and style

[nyarly at gmail.com]

I'm reasonably new to Og, although I've followed Nitro + Og for some
time.  Now that I'm digging into Og for my own purposes, I have some
questions about the way it's structured.

Mostly, I'm curious about the decision for the #enchant methods to
eval strings on the target classes.  Is there a reason to prefer this
over eval'ing a block, and doing the string interpolations in
define_method calls?  If nothing else, this buys nicer backtraces that
go through the #enchant results.