Converting to open source project

[symball]

This is a documentation status ticket to discuss / list tasks we would need to carry out prior to open sourcing the mail tester repository. Once discussion is complete, individual work will be split in to separate issues

Possible Tasks

• Rename project to mailgun-mock or something similar
• Build status / version / code quality report as "shields" at top of README such as can be found here. Also link to docs site
• Automated code quality / security tools integration such as sonatype
• Full code comment review for godoc
• Add tests where applicable
• Review README and contributions doc

[sampullman]

Originally I thought it would be interesting to expand this to include more mail services, but Mailgun has been solid for such a long time that it may not be necessary, so mailgun-mock sounds good. A more generic name like mail-api-mock works too, though it'd be a bit silly if we never extended support to other services.