Modify README.md to include new features and examples for v2

Rewrite, fix and add new examples to README.md.

This is a time consuming task and any help is greatly appreciated.

The following tasks are related to this:

[x] Add Power Apps terminology #143
[x] Describe What's New in v2 #146

List of sections to be checked/rewritten:

[x] Getting Started
[x] DynamicsWebApi as a Dynamics 365 web resource
[x] DynamicsWebApi for Node.js
[x] Configuration
[x] Configuration Parameters
[x] Request Examples
[x] Create a record
[x] Update a record
[x] Update a single property value
[x] Upsert a record
[x] Delete a record
[x] Delete a single property value
[x] Retrieve a record
[x] Retrieve multiple records
[x] Change Tracking
[x] Retrieve All records
[x] Count
[x] Count limitation workaround
[x] Associate
[x] Associate for a single-valued navigation property
[x] Disassociate
[x] Disassociate for a single-valued navigation property
[x] Fetch XML Request
[x] Fetch All records
[x] Execute Web API functions
[x] Execute Web API actions
[x] Execute Batch Operations
[x] Work with Metadata Definitions
[x] Create Entity
[x] Retrieve Entity
[x] Update Entity
[x] Retrieve Multiple Entities
[x] Create Attribute
[x] Retrieve Attribute
[x] Update Attribute
[x] Retrieve Multiple Attributes
[x] Use requests to query Entity and Attribute metadata
[x] Create Relationship
[x] Update Relationship
[x] Delete Relationship
[x] Retrieve Relationship
[x] Retrieve Multiple Relationships
[x] Create Global Option Set
[x] Update Global Option Set
[x] Delete Global Option Set
[x] Retrieve Global Option Set
[x] Retrieve Multiple Global Option Sets
[x] Work with File Fields
[x] Upload file
[x] Download file
[x] Delete file
[x] Retrieve CSDL $metadata document
[x] Formatted Values and Lookup Properties
[x] Using Alternate Keys
[x] Making requests using Entity Logical Names
[x] Using Proxy
[x] Using TypeScript Declaration Files
[x] In Progress / Feature List
[x] JavaScript Promises
[x] JavaScript Callbacks <- must be deleted
[x] Contributions

Needs to be added:

[X] Features
[X] Dataverse Search API #134
[X] CSDL $metadata document retrieval examples
[x] v2 breaking changes #135
[x] v1 to v2 migration guide - this is probably going to go to the wiki #147

AleksandrRogov / DynamicsWebApi

Modify README.md to include new features and examples for v2 #142