Fix some doc typos
Export all Object fields

This is to help transition away from Object.
Change import paths
Remove shortcut functions
Export flag constants
Disable JSON for now
Make schema compatible with v0.4 and regenerate code

This doesn't update the schema, however.
Remove unnecessary asserts and checks

The capnp compiler does type checking for us
capnpc-go: simplify int accessor writing
Move bool accessor writing to its own function
Move to v0.4 schema
Do away with Get1 and Set1 for bool fields
Use encoding/binary directly for generated int operations
Don't use Get1 or Set1 in generated code
Use encoding/binary for floats
Use encoding/binary for Which
Simplify accessor generation
Factor out settag printing
Make zerohi32 a constant
Get rid of little shortcuts

These prevent the compiler from being able to inline and perform escape
analysis.