Vendor dependencies for 0.3.0 release

vendor/ruzstd/optimizations.md

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+# Optimizations
+This document tracks which optimizations have been done after the initial implementation passed corpus tests and a good amount of fuzzing.
+
+## Introducing more unsafe code:
+These optimizations introduced more unsafe code. These should yield significant improvements, or else they are not really worth it.
+
+### Optimizing bitreader with byteorder which uses ptr::copy_nonoverlapping
+* Reverse bitreader_reversed::get_bits was identified by linux perf tool using about 36% of the whole time
+* Benchmark: decode enwik9
+
+* Before: about 14.7 seconds
+* After: about 12.2 seconds with about 25% of the time used for get_bits()
+
+### Optimizing decodebuffer::repeat with ptr::copy_nonoverlapping
+* decodebuffer::repeate was identified by linux perf tool using about 28% of the whole time
+* Benchmark: decode enwik9
+
+* Before: about 9.9 seconds
+* After: about 9.4 seconds
+
+### Use custom ringbuffer in the decodebuffer
+The decode buffer must be able to do two things efficiently
+* Collect bytes from the front
+* Copy bytes from the contents to the end
+
+The stdlibs VecDequeu and Vec can each do one but not the other efficiently. So a custom implementation of a ringbuffer was written.
+
+## Introducing NO additional unsafe code
+These are just nice to have
+
+### Even better bitreaders
+Studying this material lead to a big improvement in bitreader speed
+* https://fgiesen.wordpress.com/2018/02/19/reading-bits-in-far-too-many-ways-part-1/
+* https://fgiesen.wordpress.com/2018/02/20/reading-bits-in-far-too-many-ways-part-2/