improvements to ast_pp:  * handle List, Set, Lambda node types.  * better punctuation and whitespace for Dict.
improvements to ast_pp:
 * handle List, Set, Lambda node types.
 * better punctuation and whitespace for Dict.

hawkowl/pydoctor,jelmer/pydoctor,jelmer/pydoctor,hawkowl/pydoctor,jelmer/pydoctor