Add custom parser support #118
Description
The ParserInterface interface already exists, so why not make it exposed (with some alterations) so users can create custom parsers for custom pipes for example?
I have a pipe that changes the translation key prefix based on the environment (at runtime). The translation keys for both prefixes need to be extracted. Creating a custom parser could allow the extractor to create both keys in the json file.
A --parsers option and/or a config file to include the custom parsers in the extractor could be added.