Merge branch 'release/0.3.0'
Merge branch 'release/0.3.1'
Merge branch 'release/0.3.2'
Merge branch 'release/0.3.3'
Merge branch 'release/0.3.4'
Merge branch 'release/0.3.5'
Merge branch 'release/0.3.6'
Merge branch 'release/0.3.7'
Add some useful _StructSchema, reader, and builder methods

This adds:
 - _StructSchema.fieldnames
 - _DynamicStructBuilder.as_reader
 - _DynamicStruct{Reader,Builder}.schema and __dir__

This makes the reader and builder types much easier to navigate in ipython.
Expose _StructSchema's raw node
Add testing libraries to requirements.txt
Merge branch 'master' of https://github.com/amluto/capnpc-python-cpp into develop

Conflicts:
	capnp/capnp.pyx
	capnp/capnp_cpp.pxd