Remove stray print statement.
Implement __str__ and __repr__ for struct and list builders.  __str__ uses prettyPrint while __repr__ shows the type name and the low-whitespace stringification.  Also implement __repr__ for StructSchema, just because why not?
Add tests based on TestAllTypes from the C++ test.capnp.  Fix problems uncovered in capnp.pyx.  Requires capnproto-c++-0.3.0-rc5, as I found a bug in the base library.
Wrap MessageBuilder::setRoot().
Store Builders by value rather than allocate them separately on the heap (matches treatment of Readers).  v0.3 fixes the bug that made this not work.
Add shortcuts for reading from / writing to files.  In Python, it doesn't make much sense to force people to muck around with MessageReaders and MessageBuilders since everything is landing on the heap anyway.  Instead, let's make it easy:  MyType.read[Packed]From(file) reads a file and returns a MyType reader.  MyType.newMessage() returns a MyType builder representing the root of a new message.  You can call this builder's write[Packed]To(file) method to write it to a file.