Allow can_be_empty to be set on a per-field basis.  This is useful for CSRF tokens.
Allow Formo::add_rule() to use a syntax similar to Validation::rule().
Merge pull request #195 from shadlaws/revise_add_rule_syntax

Allow Formo::add_rule() to use a syntax similar to Validation::rule().
Merge pull request #194 from shadlaws/can_be_empty_patch

Allow can_be_empty to be set on a per-field basis. This is useful for CSRF.