GzipSource beginnings.

Should we later support random access for other primitives
or random bulk access, I'd like the prefix to stay constant
(getByte, getInt, getLong, getBytes) vs. the suffix (byteAt,
intAt, longAt). Prefixing may work better for autocomplete
in IDEs, particularly since we already use a prefix for our
consuming reads (readByte, readInt, readLong).

GzipSource exceptions used six hex digits instead of
8 to print ints.

readUtf8 always did an extra copy of the bytes being
read.

Moving bytes between buffers crashed when the destination
was empty and the source was a prefix.

InputStream reading returned values in -128..127 instead
of in 0..255.

Rename byteAt to getByte.

Fix some OkBuffer bugs.

Initial implementation of an OkHttp-backed curl clone.

OkHttp no longer uses default ssl context.

Add -X to okcurl, permitting HEAD requests

This isn't quite as simple as I had hoped. We still lack something
like DataInputStream/BufferedInputStream that combines a buffer with
a Source. That means there's a bunch of methods that must manually
refill the buffer before acting upon it.

I'm going to continue to migrate code, and will follow up with
changes to simplify this interaction.

…urce

Use OkBuffer in spdy/3 source stream.

…urce

Use OkBuffer in http/2 source stream

The Source API is nice for source implementors: no annoying
skip method, no annoying available() method, just one API to
supply bytes to the caller.

But it isn't as nice of an API for source callers. It lacks
convenient APIs!

This bridges the gap. Calling code should use BufferedSource,
and implementing code should implement Source.

BufferedSource.

Use OkBuffer in SpdyStream.