Merge pull request #62 from BottleRocketStudios/feature/headersMigrat…

…ionGuide

Added notes about `headers` property changes to migration guide

Documentation/Migrations/Hyperspace 1.x-2.0 Migration Guide.md

@@ -12,26 +12,32 @@ This guide has been provided in order to ease the transition of existing applica
 
 Hyperspace 2.0 brings a ton of refinements and improvements to the simple core functionality of Hyperspace. There are a number of new APIs in Hyperspace 2, but fortunately, most is source-compatible with Hyperspace 1.x.
 
-### Breaking Changes
+## Breaking Changes
 
-#### `NetworkRequest` and Related Types Renamed
+### `NetworkRequest` and Related Types Renamed
 
 The first API change you'll encounter is one of the few source-breaking changes. The `NetworkRequest` protocol has been deprecated and renamed to `Request`. Similarly, `AnyNetworkRequest<T>` has been deprecated and renamed to `AnyRequest<T>`. In addition the `NetworkRequestDefaults` struct has been renamed to `RequestDefaults`. The use of Xcode 9's refactor tool should make light work of this migration.
 
-#### `ErrorType` `associatedtype` Added to the `Request` Protocol
+### `ErrorType` `associatedtype` Added to the `Request` Protocol
 
 The second major change in Hyperspace 2 is the introduction of a new `associatedtype` on `Request` - `ErrorType`. In this new version, all errors returned to you are generically typed, we no longer lock you into using `AnyError`. Any custom request types you have created now have the option of replacing their usage of `AnyError` with a custom type conforming to `NetworkServiceFailureInitializable`. The usage of `AnyRequest<T>` should remain unaffected. Because we can now utilize this `NetworkServiceFailureInitializable` protocol to allow for the conversion of a `NetworkServiceFailure` into a generic error type of the consumer's choosing, we have also deprecated `BackendServiceError` and the associated `BackendServiceErrorInitializable` protocol. More information on the robust error handling capabilities of Hypersace 2.0 is available in [`Documentation/Guides/ErrorHandling.md`](../Guides/ErrorHandling.md).
 
-#### URL Query Parameters No Longer Part of the `Request` Protocol
+### URL Query Parameters No Longer Part of the `Request` Protocol
 
 In order to simplify the `Request` protocol, we've changed the way URL query parameters are handled. If your request needs to use query parameters, it's now up to use the `generateRawQueryParametersString(from:)` in the extension on `URLQueryItem` to generate a query parameter string that you can append to the end of the request's URL. We've provided an `appendingQueryString(_:)` method on `URL` to help you generate a new `URL` from the generated query string. You can also just use the `appendingQueryItems(_:using:)` method on `URL` to shortcut this two-step process. 
 
-### Other Improvements
+### `Request` Protocol `headers` Property Is Now a Stored Property
 
-#### `HTTP.Status` Converted to `RawRepresentable` Struct
+The `headers` property has changed from a `{ get }` read-only computed property to a `{ get set }` stored property. This change allowed for some helper functions regarding request headers to be added to `Request`: 
+* `addingHeaders(_:)` - Adds/merges the provided headers with the receiver's headers.
+* `usingHeaders(_:)` - Replaces the receiver's headers with the provided headers.
+
+## Other Improvements
+
+### `HTTP.Status` Converted to `RawRepresentable` Struct
 
 You can now specify custom HTTP status codes if you wish.
 
-#### Container Decoding Improvements
+### Container Decoding Improvements
 
 We've improved the way you can handle decoding containers. More information is available in [`Documentation/Guides/Custom Decoding.md`](../Guides/Custom%20Decoding.md).