docs: update READMEs with new APIs and usage examples #937

Job	Run time
parser-tests (plpgsql-deparser)	1m 5s
parser-tests (plpgsql-parser)	1m 2s
parser-tests (utils)	1m 2s
parser-tests (pgsql-cli)	56s
parser-tests (transform)	5m 52s
parser-tests (traverse)	57s
parser-tests (proto-parser)	59s
parser-tests (parser)	52s
parser-tests (deparser)	1m 0s
	13m 45s

Provide feedback