Cleaner disconnect handling.  Better fix for issue #71, and also simplifies the interface and improves robustness.

Make TwoPartyVatNetwork::onDrained() work correctly on the server side.  Previously only worked on the client side, where it's actually not very useful.  Fixes #71.  There's a deeper problem, though, that simply holding a capability received from the client will hold the dead connection open.

Fix bug where receiving EOF on the RPC connection could cause RpcConnectionState to go into an infinite promise loop.  Strange that this did not cause trouble earlier.  Also some minor tweaks.

Fixes #67.  Also, prevent people from accidentally making MessageBuilder subclasses copyable/movable as brought up in issue #64.

fix typos and inconsistencies

fix two more typos

fix two typos in the docs

Fix bounds check passing for relative struct pointers with offsets that underflow

Fix missing annotations

Fix C+1y warnings from Clang.

warning: 'constexpr' non-static member function will not be implicitly
'const' in C++1y; add 'const' to avoid a change in behavior
[-Wconstexpr-not-const]

calculator.capnp style adjusting

p.s. thanks @cstrahan for vim syntax highlighting

Delete snappy code.  It relied on an unsubmitted patch to Snappy's interface and it turns out LZ4 is better anyway so we'll probably integrate with that instead, eventually.

Upgrade gtest to 1.7.0

doc: Fix documentation pseudocode to match description.