releasenotes: update docstrings with information on additional flags This patch adds documentation related to the two new flags --check and --list for releasenotes extension. Differential Revision: https://phab.mercurial-scm.org/D544

releasenotes: raise error on simultaneous usage of flags The releasenotes command is supposed to raise an error when --list and --rev/--check flags are used together. This patch adds the above functionality. Differential Revision: https://phab.mercurial-scm.org/D831