Added a load function to the capnp module

It takes .capnp file and will load it through the C++ capnproto library.
Only major thing left is initializing lists and structs in
MessageBuilder

schema.pxd

@@ -0,0 +1,9 @@
+# schema.capnp.cpp.pyx
+# distutils: language = c++
+# distutils: extra_compile_args = --std=c++11
+# distutils: libraries = capnp
+from schema_cpp cimport Node as C_Node
+cdef class _NodeReader:
+    cdef C_Node.Reader thisptr
+    cdef init(self, C_Node.Reader other)
+