Trace compression improvements

[evel]

Hello,

This patch series improves trace compression by implementing threaded
compression offloading and providing alternative compression methods.  
The
main difference from previously implemented threaded compression is 
that
locking overhead is significantly reduced thanks to using a 
double-buffered
output buffer instead of a ring buffer that was locked on each call 
dump
operation.

https://github.com/Testiki/apitrace/tree/threaded-file