Move doc folder to the root to make it more accessible

[MAILPOET-4107]

doc/api_methods/AddSubscriberField.md

@@ -5,7 +5,7 @@
 ## `array addSubscriberField(array $data)`
 
 Using this method you can create custom properties that can be used for storing additional data for each subscriber.
-See [Subscriber Fields for more details](./GetSubscriberFields.md)
+See [Subscriber Fields for more details](GetSubscriberFields.md)
 
 ## Arguments
 

doc/api_methods/GetSubscriberFields.md

@@ -7,7 +7,7 @@
 Each subscriber has a set of default properties (`email`, `first_name`, `last_name`).
 MailPoet enables the extension of these properties by adding custom properties.
 This method returns list of all properties available for a subscriber (default + custom).
-See also [addSubscriberField function.](./AddSubscriberField.md)
+See also [addSubscriberField function.](AddSubscriberField.md)
 
 ## Subscriber Field
 

doc/api_methods/SubscribeToList.md

@@ -6,4 +6,4 @@
 
 This method allows adding an existing subscriber into a list, and handles confirmation email and admin notification email sending.
 
-This method works exactly the same as [Subscribe to lists](./SubscribeToLists.md). The only difference is the second argument which is a single list id.
+This method works exactly the same as [Subscribe to lists](SubscribeToLists.md). The only difference is the second argument which is a single list id.

doc/api_methods/UnsubscribeFromList.md

@@ -6,4 +6,4 @@
 
 This method removes a subscriber from given list.
 
-This method works exactly the same as [Unsubscribe from Lists](./UnsubscribeFromLists.md). The only difference is the second argument which is a single list id.
+This method works exactly the same as [Unsubscribe from Lists](UnsubscribeFromLists.md). The only difference is the second argument which is a single list id.