cfengine.el: update for the upcoming CFEngine 3.7 release

cfengine.el: update for the upcoming CFEngine 3.7 release

Update for the upcoming CFEngine 3.7 release: support macros and
quoted context strings; reformat JSON; indent promise attributes 2
units by default; give function parameter descriptions in the eldoc
glue.
* cfengine.el: Update version and docs and fix name.  Autoload
`json-pretty-print'.  Support new features in 3.7.
(cfengine-parameters-indent): Set default promise attribute indent to
2 more than the promise itself.
(cfengine3-macro-regex): New variable to match the new macro syntax.
(cfengine3-font-lock-keywords): Use it to highlight macros.
(cfengine3-indent-line): Use it to indent macros to column 0.
(cfengine3-class-selector-regex): Update for the new quoted strings
format.
(cfengine3-reformat-json-string): New function to reformat a JSON
string using `json-pretty-print'.
(cfengine3-format-function-docstring): Use function parameter
description if it's provided by the cf-promises syntax dump.