feat(mail): add the possibility to send the repport by emails.

Add command line options and configuration possibilities for:
- email to
- email from
- email subject

Only the 'email to' line is required in order for an email to be sent.
feat(use config section): add the hability to easily use a specific config section in the command line.
feat(config): can now use a config file (with a provided section) to filter stdin.
feat(config): add the possibility to include a section into another.
doc(README): update README with a section about configuration.