added some additional documentation

docs/dev_doc.md

@@ -0,0 +1,4 @@
+# Developer documentation
+
+This documentation is mainly for developers who wish to create a third party
+module

docs/index.rst

@@ -3,11 +3,11 @@
    You can adapt this file completely to your liking, but it should at least
    contain the root `toctree` directive.
 
+Inkycal documentation
+======================
 .. image:: ../Gallery/logo.png
    :align: center
 
-Inkycal documentation
-======================
 .. toctree::
    :maxdepth: 2
    :caption: Contents:
@@ -15,6 +15,7 @@ Inkycal documentation
    inkycal
    about
    quickstart
+   dev_doc
 
 Indices and tables
 ==================

docs/inkycal.rst

@@ -16,3 +16,10 @@ Custom functions
 .. automodule:: inkycal.custom.functions
   :members:
 
+Helper classes
+=================
+.. automodule:: inkycal.modules.ical_parser
+  :members:
+
+.. automodule:: inkycal.modules.inky_image
+  :members: