Add `as_builder` method to Struct Reader
Add `as_builder` method to Struct Reader

tempbottle/pycapnp,rcrowder/pycapnp,rcrowder/pycapnp,SymbiFlow/pycapnp,tempbottle/pycapnp,SymbiFlow/pycapnp,jparyani/pycapnp,SymbiFlow/pycapnp,SymbiFlow/pycapnp,jparyani/pycapnp,tempbottle/pycapnp,rcrowder/pycapnp,jparyani/pycapnp,jparyani/pycapnp,rcrowder/pycapnp,tempbottle/pycapnp