Add email communication service/medium

[scastlara]

Is your feature request related to a problem? Please describe.
We now send reports to Slack. We should add an option to send reports by email.

Describe the solution you'd like
A set of cli opts that allows sheriff to send reports to email as an alternative to Slack.

• Global level report
• Project level report

Describe alternatives you've considered
...

Additional context
see #10 for the discussion

[scastlara]

https://en.wikipedia.org/wiki/Mailto