Merged FAD-3148 into 2.x

* FAD-3148 basic non-functioning base class

* FAD-3148 a bit more functionality in the base class

* FAD-3148 added custom promise class and custom response class. Did good things to SparkPost class

* Updated Transmission.php for new refactor, still WIP. Created Resource.php as a parent class for all future resources.

* Removed test functions

* Cleaned up Transmissions.php according to PSR-2, deleted more test code and comments.

* added sync and aysnc, cleaned up code

* added support for async/sync option

* added support for async/sync option

* Added interns to authors

* simplified the request function

* added comments

* added user agent

* added comments in SparkPostPromise

* added comments in SparkPostException

* added comments in SparkPostResponse

* cleaning up test

* updated composer.json and contributing files for testing

* Ran php-cs-fixer

* testing for sparkpost response class

* updated to newer version of guzzle

* updated to newer version of guzzle

* Cleaned up getUrl and other functions

* cleaned up constructor and overrode getCode with getResponse()->getStatusCode()

* fixed up then method

* cleaned up getBody

* deleted old test

* Wrote total coverage tests for SparkPost class

* commented out setting up transmissions endpoint until merging with FAD-3146

Author: avigoldman

Diff for: .gitignore

@@ -6,3 +6,4 @@ test/output/
 examples/example-config.json
 .idea
 /composer.phar
+test.php

Diff for: AUTHORS.md

@@ -13,3 +13,5 @@ php-sparkpost is maintained by Message Systems.
 * Chris Wilson, [@yepher](https://github.com/yepher)
 * Maxim Dzhuliy, [@max-si-m](https://github.com/max-si-m)
 * [@chandon](https://github.com/chandon)
+* Avi Goldman, [@avrahamgoldman](https://github.com/avrahamgoldman)
+* Vincent Song, [@vwsong](https://github.com/vwsong)

Diff for: CONTRIBUTING.md

@@ -26,7 +26,7 @@ Add composer install directory to $PATH `~/.composer/vendor/bin/`
 
 #### Install PHPUnit for Testing
 ```
-composer global require "phpunit/phpunit=4.3.*"
+composer global require "phpunit/phpunit=4.8.*"
 ```
 
 We recommend increasing PHP’s memory limit, by default it uses 128MB.  We ran into some issues during local development without doing so.  You can do this by editing your php.ini file and modifying `memory_limit`.  We set ours to `memory_limit = 1024M`.

Diff for: composer.json

@@ -16,19 +16,19 @@
   },
   "require": {
     "php": ">=5.5.0",
-    "egeloen/http-adapter": "*"
+    "php-http/client-implementation": "^1.0",
+    "guzzlehttp/psr7": "1.3.*"
   },
   "require-dev": {
-    "phpunit/phpunit": "4.3.*",
     "guzzlehttp/guzzle": "6.*",
+    "php-http/guzzle6-adapter": "*",
+    "php-http/message": "*",
     "mockery/mockery": "^0.9.4",
-    "satooshi/php-coveralls": "dev-master",
     "fabpot/php-cs-fixer": "^1.11"
   },
   "autoload": {
     "psr-4": {
       "SparkPost\\": "lib/SparkPost/",
-      "SparkPost\\SendGridCompatibility\\": "lib/SendGridCompatibility/",
       "SparkPost\\Test\\TestUtils\\": "test/unit/TestUtils/"
     }
   }