[0.4.0] Dec-02-2019

Additions

• [Issue #31] Add documentation about accessing Mailgun member directly
• [Issue #29] Add send() options parameter
• [Issue #28] Add npm keywords
• [Issue #27] Add Mailgun custom options

Fixes

• [Issue #26] Change host to 'api.eu.mailgun.net'
• [Issue #25] Update TravisCI Node version
• [Issue #10] Should not call list api in testMode
• npm update