support standard brotli compression/decompression (.br format compressible with single-threaded brotli)

[sebres]

This PR implements support for standard brotli compression/decompression without 7z container, header and framing (.br format compressible with single-threaded brotli API or command line tool).

Usage examples for 7z command line:

# compress:
7z a -tbrotli -mx4 -mwlog=24 archive.txt.br file-to-compress.txt

# test (with SHA256):
7z t -scrcSHA256 archive.txt.br

# decompress:
7z e archive.txt.br -so > uncompressed-file.txt

Because brotli handler also uses BrotliEncoder/BrotliDecoder but they using brotli-mt in 7z format, also with -mmt=1, to compress/decompress single-threaded brotli format the handler uses threads=0 internally. This is artificial value and signals that standard brotli compression format (without headers and mt-frames according to RFC 7932) must be used.
However by decompression one could read the header and check whether BROTLIMT_MAGIC_SKIPPABLE is available, just brotli format is complex and it doesn't really has a header prefix, so one can't exclude that at some point some compressed file or stream wouldn't start with the same bits sequence equal to BROTLIMT_MAGIC_SKIPPABLE.
So at the moment only file extension (.br, .brotli) or parameter -tbrotli determine the type of brotli compression format.

Additionally brotli encoder extended now to support supplying of wlog and long parameters, in 7z (-m0=brotli:long=n) as well as in brotli format.

Related to #21, #126