This small addon binds the first ten keys of the default flyout buttons to keys 1, 2, 3, etc to 0 while the flyout is open. When the flyout closes, the keys revert to their usual action.
Hunter traps, warlock pets, mage portals, warrior banners, and several other groups of spells have flyout buttons in the spellbook. Clicking them (or hitting their binding if dragged to your bars) will open the flyout to choose a spell within. This addon binds the first ten buttons to keys so you don't need to click the spells within the flyout to cast.
(For more commonly used spells within a flyout, you can drag the spell from within the flyout to an action button. No addon is required to do this.)