rbperf v0.2.1

Changes

Now rbperf is also shipped as a statically linked binary. Until now, libc and other libraries were required in the system, which was a problem in some distros that shipped older, incompatible versions. There's an added CI job to ensure that the static build works
Enabled LTO for release builds, reducing binary size enough to produce binaries with the same size even though now they are statically linked
Fixes to allow profiling Ruby processes that are statically linked, rather than dynamically linking libruby