Add CFEngine 3 ElDoc, completion, and compilation glue to cf-promises.

Add CFEngine 3 ElDoc, completion, and compilation glue to cf-promises.

* progmodes/cfengine.el: Version bump.
(cfengine-cf-promises): New defcustom to locate cf-promises.
(cfengine3-vartypes): Add new "data" type.
(cfengine3--current-word): New function to get current name-like
word or its bounds.
(cfengine3--current-function): New function to look up a CFEngine
function's definition.
(cfengine3-format-function-docstring): New function.
(cfengine3-make-syntax-cache): New function.
(cfengine3-documentation-function): New function: ElDoc glue.
(cfengine3-completion-function): New function: completion glue.
(cfengine3-mode): Set `compile-command',
`eldoc-documentation-function', and add to
`completion-at-point-functions'.