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.