Add a ton of docstrings and add to official docs

docs/capnp.rst

@@ -26,10 +26,51 @@ Readers
   :undoc-members:
   :inherited-members:
 
-Writers
+Builders
 -------------
 
+.. autoclass:: MessageBuilder
+  :members:
+  :undoc-members:
+  :inherited-members:
+
 .. autoclass:: MallocMessageBuilder
   :members:
   :undoc-members:
   :inherited-members:
+
+Internal Classes
+----------------
+These classes are internal to the library. You will never need to allocate 
+one yourself, but you may end up using some of their member methods.
+
+Readers
+~~~~~~~~~~
+.. autoclass:: _DynamicStructReader
+  :members:
+  :undoc-members:
+  :inherited-members:
+
+.. autoclass:: _DynamicListReader
+  :members:
+  :undoc-members:
+  :inherited-members:
+
+Builders
+~~~~~~~~~~
+.. autoclass:: _DynamicStructBuilder
+  :members:
+  :undoc-members:
+  :inherited-members:
+  
+.. autoclass:: _DynamicListBuilder
+  :members:
+  :undoc-members:
+  :inherited-members:
+
+Miscellaneous
+~~~~~~~~~~~~~
+.. autoclass:: _DynamicOrphan
+  :members:
+  :undoc-members:
+  :inherited-members: