Allow to override message.from via send options

[peterpetre]

Please allow to pass message.from on send options and this should override the this.config.message.from

[niftylettuce]

@peterpetre care to submit a pull request + test?

[peterpetre]

@niftylettuce #319 is ok?

[niftylettuce]

Since this would be a breaking change, I think I'll publish with major semver version, agreed?

[niftylettuce]

@peterpetre I have just merged your work. I updated the README and added a new section here https://github.com/niftylettuce/email-templates#v5-breaking-changes (might need a bit more explaining with an example - if you care to submit a PR to update this README with a code example that shows before/after issue that would be great). email-templates@5.0.0 has been published to NPM. Let me know if you have any issues, and thank you for your contributions to this project 👏 🎉