Add a section on lambda's.

Dissuade their use when named function is better.
Prohibit quoting.
Move existant lambda information into section.

This will conflict with #12 . I'll rebase locally if #12 is merged here.
You're right, maintainability isn't an issue in that case, but readability still is. And in the case of defcustom, you're exposing a rough lambda to a large range of less-savvy users, where you could be exposing a reasonable name of a well documented function.

But I agree it's important to be reasonable. We could recommend a named function, instead of saying it's wrong.