Switchted to Mialchimp transactional API

What's Changed

• Moved send test, fixed #27, #35 by @simialbi in #36
• Code style updates, test updates by @simialbi in #39
• Added "send at" and "ip pool" feature by @simialbi in #40

Full Changelog: 1.8.1...2.0.0

Added `send_at` and `ip_pool` options

Added "send at" and "ip pool" feature (#40)

* fixed "RequestException"

Replaced mandrill dependency with mailchimp-transactional

Moved send test, fixed #27, #35 (#36)

* changed from travis to git action
* used new env setting method
* fixed brackets
* updated dependencies
* updated unit tests
* updated MandrillTest.php added runtime directory creation
* fixed metadata class var, code style updates, 
added ext-fileinfo to composer.json
* tests with key from secrets

* tests with key from secrets 2

* tests with key from secrets 3

* fixed response and error handling

* fixed logging

* replaced sendRaw with send

* set global merge vars and template content independent from template language
fixed response handling

* fixed test

* fixed message test

Fixed #33, #34

• Fixed Array and string offset access syntax with curly braces is deprecated error

1.8.0

Added new key features

Change Log

• Applied yii2 code styles
• Added local merge vars
• Added metadata property
• Added recipient metadata property
• Added google analytics domains property
• Added google analytics campaign property

1.7.0

added the option to retrieve the original mandrill response.
now sub accounts can be set and you can specify directly the project
you can also specify whether or not you want to enable clicks and opens tracking and if the message is important.
a general clean up of the project has been performed.