Add more Python-visible reflection

This is probably not the most efficient thing in the world, nor is it
really beautiful, but it's fun.  Now you can do this in ipython with
liberal use of the tab key:

In [2]: import capnp

In [3]: s = capnp.load('/home/luto/devel/capnp/test.capnp')

In [4]: s.
s.CxxgenArgs   s.Double2D     s.ExpRanges    s.Exposures    s.StaticState  s.cxxgen       s.fxgraphnode  

In [4]: s.Double2D.Schema
Out[4]: <capnp.capnp._StructSchema at 0x29a2e60>

In [5]: s.Double2D.Schema.
s.Double2D.Schema.fieldnames  s.Double2D.Schema.node        

In [5]: s.Double2D.Schema.node
Out[5]: <capnp.capnp._DynamicStructReader at 0x299d1b8>

In [6]: s.Double2D.Schema.node.
s.Double2D.Schema.node.annotation               s.Double2D.Schema.node.id
s.Double2D.Schema.node.annotations              s.Double2D.Schema.node.interface
s.Double2D.Schema.node.const                    s.Double2D.Schema.node.nestedNodes
s.Double2D.Schema.node.displayName              s.Double2D.Schema.node.schema
s.Double2D.Schema.node.displayNamePrefixLength  s.Double2D.Schema.node.scopeId
s.Double2D.Schema.node.enum                     s.Double2D.Schema.node.struct
s.Double2D.Schema.node.file                     s.Double2D.Schema.node.which

Andy Lutomirski (2):
  Add some useful _StructSchema, reader, and builder methods
  Expose _StructSchema's raw node

 capnp/capnp.pyx     | 42 ++++++++++++++++++++++++++++++++++++++++++
 capnp/capnp_cpp.pxd | 14 +++++---------
 2 files changed, 47 insertions(+), 9 deletions(-)