Remove callbacks

Why:

There is a lot of code we maintain to support callbacks. There is also
inconsistent support for usage throughout the codebase. Any users of the
library can achieve the same behavior as a callback by leveraging the
promises we return from api calls.

This PR:

Removes callback support.

History.md

@@ -1,30 +1,42 @@
-1.0.0 / 2017-08-23
-==================
+# 2.0.0 / 2018-12-19
 
-  * Added support for promises
-  * Added support for OAuth2
-  * Added convenience methods to support OAuth
-  * Tests working on demo instance of HubSpot
-  * Added support for some missing methods
+- Begins migration of test suite to mocked api calls instead of hitting HubSpot
+  "live"
+- Added support for some api endpoints such as timelines.
 
 Breaking changes:
-  * New instantation of client
-  * node > 6.10.0 required (see below)
+
+- Remove support for passing callbacks
+
+The usage of callbacks throughout node-hubspot was inconsistent in
+functionality. There was a lot of code to maintain callback support that we can
+remove now that promises are returned by all functions.
+
+# 1.0.0 / 2017-08-23
+
+- Added support for promises
+- Added support for OAuth2
+- Added convenience methods to support OAuth
+- Tests working on demo instance of HubSpot
+- Added support for some missing methods
+
+Breaking changes:
+
+- New instantiation of client
+- node > 6.10.0 required (see below)
 
 Notes:
 
-  * new version is ES2015 heavy and has only been tested in version of node > 6.10.0
-  * hasn't been tested in browser
-  * some babel magic would be needed for use in older versions of node (PR welcome!)
+- new version is ES2015 heavy and has only been tested in version of node > 6.10.0
+- hasn't been tested in browser
+- some babel magic would be needed for use in older versions of node (PR welcome!)
 
-0.3.0 / 2016-03-29
-==================
+# 0.3.0 / 2016-03-29
 
-  * Removed events.get() and campaigns.tracking.events() by merging them into campaigns.events()
+- Removed events.get() and campaigns.tracking.events() by merging them into campaigns.events()
 
-0.2.5 / 2016-03-25
-==================
+# 0.2.5 / 2016-03-25
 
-  * Added client.files.getOne()
-  * Fixed client.files.get()
-  * Updated README
+- Added client.files.getOne()
+- Fixed client.files.get()
+- Updated README