* guix/scripts/style.scm (canonicalize-comment): New procedure.
(pretty-print-with-comments): Add #:format-comment. and honor it.
(object->string*): Add 'args' and honor them.
(format-package-definition): Pass #:format-comment to
'object->string*'.
* tests/style.scm ("pretty-print-with-comments, canonicalize-comment"):
New test.
This allows us to express cases where a newline should be inserted
immediately after the head symbol of a list.
* guix/scripts/style.scm (%newline-forms): New variable.
(newline-form?): New procedure.
(pretty-print-with-comments): Handle "newline forms".
* tests/style.scm: Add test.
* guix/scripts/style.scm (vhashq): New macro.
(%special-forms): New variable.
(special-form?): New procedure.
(pretty-print-with-comments): Add many clauses and tweak existing
rules.
* tests/style.scm (test-pretty-print): New macro.
<top level>: Add 'test-pretty-print' tests.
