Migrate to grammY 2.0

This plugin needs to be migrated to grammY 2.0.

It should also absorb the functionality of the parse-mode plugin, which it replaces, as per https://t.me/grammyjs/373074. See grammyjs/parse-mode#61.

See grammyjs/grammY#709 for the context flavour rework, and grammyjs/grammY#675 for the overall roadmap. Background: https://t.me/grammyjs_news/98

Start by reading the grammY 2.0 migration context in grammyjs/grammY#709 and #675, then review grammyjs/parse-mode#61 and the linked announcement. Identify the plugin entry points and current parse-mode integration before defining the migration scope. Done means the plugin works with grammY 2.0 and includes the replaced parse-mode functionality.

Written by the indexing model from the issue text.