DELAY CORE ATTRIBUTE INIT

We might want something like $zilla->name to come from some plugin that converts from main_module, or yadda yadda. This will allow register-on-the-fly of plugins because we can construct the Zilla before we know all its required attribute values.

We'll probably mark those values as LazyRequired and SetOnce.

ATTRIBUTES TO FIX, IN ORDER:

• main_module, name -- interdependent

• abstract

• version - it's unique and should be simplified

• copyright_{holder,year} - should come from a plugin somehow, too
• license

• authors

• root?