Old doc links (#45)

Fixes #43

extend/api.md

@@ -9,4 +9,4 @@ InvenTree ships with an extensive REST API that is used by several native applic
 - InvenTree App (Android/iOS)
 - python module
 
-The API is self-documenting. More information is provided in the [documentation](https://inventree.readthedocs.io/en/latest/api/api/).
+The API is self-documenting. More information is provided in the [documentation](https://docs.inventree.org/en/latest/api/api/).

extend/app.md

@@ -26,4 +26,4 @@ The InvenTree app can be downloaded from either the Android or Apple app stores,
 
 ### Documentation
 
-Mobile app documentation can be found on the [InvenTree documentation site](https://inventree.readthedocs.io/en/latest/app/app/).
+Mobile app documentation can be found on the [InvenTree documentation site](https://docs.inventree.org/en/latest/app/app/).

extend/index.md

@@ -8,4 +8,4 @@ InvenTree is designeds to be part of a larger system of tools to support both ho
 - [API](api)
 - [Integrate](integrate) into other tools
 - PK2InvenTree for [migrating from PartKeepr to InvenTreen](https://github.com/rgilham/PK2InvenTree)
-- Python [package](https://inventree.readthedocs.io/en/latest/extend/python/) 
+- Python [package](https://docs.inventree.org/en/latest/extend/python/) 

extend/plugin/index.md

@@ -2,7 +2,7 @@
 title: Plugins
 ---
 We supply core-dev and community built plugins to get you started with extending InvenTree's functionality. Plugins can hook into many parts of the UI, buisness logic and webserver.
-We expose some internal python APIs to speed up your development and keep the instance running while you discover the possibilities. [Learn more](https://inventree.readthedocs.io/en/latest/extend/plugins/)
+We expose some internal python APIs to speed up your development and keep the instance running while you discover the possibilities. [Learn more](https://docs.inventree.org/en/latest/extend/plugins/)
 
 ### Highlights