[roundtrip_test.py] repeat test at different quality (1, 6, 9, 11)

Expose the quality parameter to the bro.cc tool.

Use the same hasher for text and font mode.

We use 4-byte hashing in both and look for length 3
matches separately.

Fix broken quality 0, make it same as quality 1.

[python] expose new encoder parameters as kwargs of brotli.compress

remove additional low-level parameters

modified the help string to include the new parameters.

renamed variables: transform -> enable_transforms, dictionary -> enable_dictionary

update brotli.compress docstring accordingly

Add a MODE_GENERIC compression mode to the interface.

With this the users can distinguish between not knowing
what the input is (ddefault) and knowing that it is text,
and thus can be relied on to force some UTF-8 specific settings.

[python] fix compatibility_test.py with Python 3

In python3, the 'string' module no longer has a 'split' function.

Handle multiple compressed files per original in the test.

Add some more test cases that decompress to the empty
file or a one byte long file. These test cases have
examples for the updated stream header and meta-block
header formats.

Restrict the ARM optimizations to little endian architectures.

Add an Acknowledgements section to the spec.

Fix 32bit build.

Support window bits 10 - 15 in the decoder.

The previous window bit value 17 is used to
extend the range, since it has not been used
in any previous encoders.

Align distance code meaning in the brotli encoder.

Two different definitions (offset by 1) were used in
command.h and hash.h. Now they have been made the same,
also consistent with the spec (e.g. 0 means use previous dist, etc...)

Faster encoding for low quality settings.

With this commit, the encoder will skip some
compression optimization steps for quality <= 4,
which results in faster compression but higher
compressed sizes.

Use a static context map with two buckets for UTF8 data.