Support varint-encoded length-delimited buffers.

Official Google Protocol Buffers support varint-encoded
length-delimited message streams.

For comparison, see the following:

    1. AbstractMessageLite#writeDelimitedTo
    2. AbstractMessageLite#mergeDelimitedFrom
Code Review: Simplify delimited decoding.

This code review addresses @bernerdschaefer's comments about
simplifying the decoding process.
Merge pull request #29 from matttproud/feature/coding/delimited-streams

Support varint-encoded length-delimited streams.