JSON: encode NaNs and infinite floats as `null`

Minor cleanup

setup-autotools.sh is no longer needed as of 6cd25260.

The instructions work without having Subversion installed as well.

Requested by jo_liss on Twitter:

https://twitter.com/jo_liss/status/664884038252027905

(Also implement defaultValue<>() helper which was defined but apparently never implemented.)

Such values are not allowed by the JSON spec. We match the behavior of
JSON.stringify in Firefox and Chrome.

fixes https://github.com/sandstorm-io/capnproto/issues/261

Fix UnixEventPort value on 32-bit big endian archs

toRegularSiginfo attempts to convert signalfd_siginfo.ssi_ptr (a 64-bit
integer across all architectures) to a pointer. On 32-bit big endian
architectures, sival_int/sival_ptr will be stored in the high 32-bits
of the ssi_ptr value.

Prior to this change, the value was "lost" as we cast away the high
bits of ssi_ptr in the conversion to a 32-bit pointer.

This fixes AsyncUnixTest::SignalWith{,Pointer}Value on affected archs.

Fix some documentation typos.

Fix typo in documentation

Add TextCodec to expose an API for the schema's text format.

Spellcheck the styleguide

Typo found by @mquandalle

Mentioned three days ago, didn't want it to get forgotten

Fix typo in two party RPC docs

Make sure ArrayPtr<char> stringifies the same as ArrayPtr<const char> (without commas after each character)

Use ip4 sockets for wildcard on OpenBSD

Short-term fix for #220.