Documentation fixes according to review

Author: iv-mexx

Documentation/FrameworkOverview.md

@@ -144,7 +144,7 @@ The current value of a property can be obtained from the `value` getter. The
 the property’s current value, followed by all changes over time. The `signal` getter returns a [signal](#signals) that will send all changes over time, but not the initial value.
 
 The `<~` operator can be used to bind properties in different ways. Note that in
-all cases, the target has to be a [`BindingTarget`][BindingTarget], [`MutableProperty`][MutableProperty] is the only property that implements this.
+all cases, the target has to be a binding target, represented by the [`BindingTargetProtocol`][BindingTarget]. All mutable property types, represented by the  [`MutablePropertyProtocol`][MutableProperty], are inherently binding targets.
 
 * `property <~ signal` binds a [signal](#signals) to the property, updating the
   property’s value to the latest value sent by the signal.

ReactiveSwift.playground/Pages/Property.xcplaygroundpage/Contents.swift

@@ -67,7 +67,7 @@ scopedExample("Creation") {
  ### Binding
 
  The `<~` operator can be used to bind properties in different ways. Note that in
- all cases, the target has to be a [`BindingTarget`](https://github.com/ReactiveCocoa/ReactiveSwift/blob/master/Sources/UnidirectionalBinding.swift) , [`MutableProperty`](https://github.com/ReactiveCocoa/ReactiveSwift/blob/master/Sources/Property.swift#L28) is the only property that implements this.
+ all cases, the target has to be a binding target, represented by the [`BindingTargetProtocol`](https://github.com/ReactiveCocoa/ReactiveSwift/blob/master/Sources/UnidirectionalBinding.swift). All mutable property types, represented by the  [`MutablePropertyProtocol`](https://github.com/ReactiveCocoa/ReactiveSwift/blob/master/Sources/Property.swift#L28), are inherently binding targets.
 
  * `property <~ signal` binds a [signal](#signals) to the property, updating the
  property’s value to the latest value sent by the signal.

ReactiveSwift.playground/contents.xcplayground

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
-<playground version='6.0' target-platform='osx' display-mode='rendered'>
+<playground version='6.0' target-platform='osx' display-mode='raw'>
     <pages>
         <page name='Sandbox'/>
         <page name='SignalProducer'/>