Deprecates helper functions and replaces with scalable alternative.

#### What's this PR do?

* Removes all helper methods
* Creates a __request method abstraction
* Creates a post and get helper method wrapper for the __request method
* Adds messages and profile_update example

**Note - I cannot properly test this as I do not have working MC credentials**

#### How should this be manually tested?

* Update your user credentials in `examples/messages.js`
* Run `node examples/messages.js`

#### Any background context you want to provide?

It will be way to hard to support all new endpoint methods moving forward. 

#### What are the relevant tickets?

Fixes #41 
Fixes #25
Fixes #24 
Fixes #23 
Fixes #22 
Fixes #21 
Fixes #20 
Fixes #19 
Fixes #18 
Fixes #17 
Fixes #16 
Fixes #15 
Fixes #14 
Fixes #13 
Fixes #12 
Fixes #11 
Fixes #10 
Fixes #9 
Fixes #8 
Fixes #7 
Fixes #6 

#### Release Type:
- [X] Major
- [ ] Minor
- [ ] Patch

cc: @jonuy @tongxiang @DeeZone 
remove comma after `_PASSWORD` here too