* hydra.el (hydra-base-map): Model after `universal-argument-map'; all
Hydra keymaps will inherit from this one.
(hydra-curr-map): Current Hydra keymap. This is necessary for
e.g. `hydra--digit-argument' to return to the orignial keymap.
(hydra--universal-argument): New function.
(hydra--digit-argument): New function.
(hydra--negative-argument): New function.
(hydra--hint): Fix dangling `body-color'.
(defhydra): keymap will inherit `hydra-base-map'.
`hydra-current-map' will be set by red heads. In red heads, make the
function call after `set-transient-map' so that e.g. "Beginning of
buffer" error will not exit the Hydra.
* hydra-test.el: Update tests.
Fixes#13.
Oleh Krehel