Replace implementation with Aircompressor code

[dain]

The core compression and decompression code has been replaced with the latest code from Aircompressor. The existing interfaces have been retained where possible. The notable exceptions:

• The deprecated SnappyInputStream and SnappyOutputStream output stream implementations have been removed. Any existing data in these formats should be converted to the specification defined framed formats using an older version of this library.
• Little endian is no longer supported
• The minimum Java version is now 1.8

[dain]

@Marcono1234 this PR brings iq80 snappy in line with aircompressor

[Marcono1234]

This also drops support for big endian CPUs (which would currently be using SlowMemory), right?

Maybe another alternative would be to always use SlowMemory, and never UnsafeMemory. This would probably keep the same functionality, but maybe this performance decrease is not acceptable. Though on the other hand this at least solves the issue, and users are encouraged to migrate to Aircompressor anyway.

Or alternatively, fix only the missing / incorrect checks which cause the issue. But I will probably test again then if there are any remaining similar issues (and I cannot guarantee that I won't overlook something).

(Though of course in the end it is your decision, so consider everything I wrote above only as suggestion please.)

[dain]

Honestly there are so few modern shipping systems that are big endian (PPC and s390x), I don't think it is worth the effort. If someone really complained loudly, I could likely add it back.

BTW, I considered just patching the problems, but I haven't looked at this repository in ages. Like it was Java 1.6, and I can't even download a JVM for that on my machine. Really, folks should upgrade, so I made this change so it will be easy to copy any future CVE fixes from aircompressor.