Close #94: obsolete comment in rpc.capnp

fix help message in capnpc-c++

fix typos and remove unused declaration

Fixes #90. The bug causes floating-point fields with non-zero defaults to be corrupted if they are set to NaN on a MIPS machine.

Added 'name' annotation for the C++ annotation to override the basename ...

The previous organization inappropriately made it seem like some implementations weren't ready for production even though they are actually being used in large-scale production already. The problem is that these projects haven't actually implemented 100% of the spec, but they have no need to, because what they have is good enough for their purposes, so their categorization was unlikely to change. I've now simply classified implementations as "Serialization + RPC" vs. "Serialization only", which seems like the most that can be said without getting subjective and ambiguous.

Explicitly mark IndexingIterator as a RandomAccessIterator

Only available when KJ_STD_COMPAT is defined.

Use absolute import path for c++.capnp

This allows {schema,rpc,rpc-twoparty}.capnp to be used without modification when
relocated outside of the Cap'n Proto codebase.

Add loadCompiledTypeAndDependencies() to SchemaParser so that compiled constants can be cast to static types.

Add ability to truncate a list post-allocation and reclaim space. Currently limited to blobs and can only be accessed through the Orphan interface.

I decided that consistent output across platforms is an important property, worth sacrificing a little bit of performance on MIPS.