Implemented Ruby fuzzing (#3339)

This PR implements fuzzing for Ruby library using https://github.com/trailofbits/ruzzy, a coverage-guided fuzzer for pure Ruby code and Ruby C extensions based on libFuzzer. Implemented binary, compact, and JSON protocol fuzzers.

A separate PR will follow to address OOM and a crash caused by unchecked memory allocation in structs (Edit: #3340).
diff --git a/lib/rb/Makefile.am b/lib/rb/Makefile.am
index ab5d903..fd5218f 100644
--- a/lib/rb/Makefile.am
+++ b/lib/rb/Makefile.am
@@ -19,6 +19,12 @@
 
 DESTDIR ?= /
 
+SUBDIRS = .
+
+if WITH_TESTS
+SUBDIRS += test/fuzz
+endif
+
 if HAVE_BUNDLER
 
 all-local: