The LZ77 portion of DEFLATE is relatively self-contained. For the
decompression side of things, we extract this logic out for the
following reasons:
* It is easier to test just the LZ77 portion of the logic.
* It reduces the noise in the inflate.go

Also, we adjust the way that callbacks are handled in the inflate.
Instead of using functions to abstract the logical componets of
huffmanBlock(), use goto statements to jump between the necessary
sections. This is faster since it avoids a function call and is
arguably more readable.

benchmark                              old MB/s     new MB/s     speedup
BenchmarkDecodeDigitsSpeed1e4-4        53.62        60.11        1.12x
BenchmarkDecodeDigitsSpeed1e5-4        61.90        69.07        1.12x
BenchmarkDecodeDigitsSpeed1e6-4        63.24        70.58        1.12x
BenchmarkDecodeDigitsDefault1e4-4      54.10        59.00        1.09x
BenchmarkDecodeDigitsDefault1e5-4      69.50        74.07        1.07x
BenchmarkDecodeDigitsDefault1e6-4      71.54        75.85        1.06x
BenchmarkDecodeDigitsCompress1e4-4     54.39        58.94        1.08x
BenchmarkDecodeDigitsCompress1e5-4     69.21        73.96        1.07x
BenchmarkDecodeDigitsCompress1e6-4     71.14        75.75        1.06x
BenchmarkDecodeTwainSpeed1e4-4         53.15        58.13        1.09x
BenchmarkDecodeTwainSpeed1e5-4         66.56        72.29        1.09x
BenchmarkDecodeTwainSpeed1e6-4         69.13        75.11        1.09x
BenchmarkDecodeTwainDefault1e4-4       56.00        60.23        1.08x
BenchmarkDecodeTwainDefault1e5-4       77.84        82.27        1.06x
BenchmarkDecodeTwainDefault1e6-4       82.07        86.85        1.06x
BenchmarkDecodeTwainCompress1e4-4      56.13        60.38        1.08x
BenchmarkDecodeTwainCompress1e5-4      78.23        82.62        1.06x
BenchmarkDecodeTwainCompress1e6-4      82.38        86.73        1.05x

Change-Id: I8c6ae0e6bed652dd0570fc113c999977f5e71636
Reviewed-on: https://go-review.googlesource.com/16528Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>