Implement greedy versioning. Refactor versioning logic. (#10)

* Implement eager versioning. Refactor versioning logic.

* Add --version-limit and --greedy-versioning command-line args

yjit.h

@@ -30,12 +30,20 @@ typedef struct rb_iseq_struct rb_iseq_t;
 #endif
 
 struct rb_yjit_options {
+    // Enable compilation with YJIT
     bool yjit_enabled;
 
     // Number of method calls after which to start generating code
     // Threshold==1 means compile on first execution
     unsigned call_threshold;
 
+    // Generate versions greedily until the limit is hit
+    bool greedy_versioning;
+
+    // Maximum number of versions per block
+    // 1 means always create generic versions
+    unsigned version_limit;
+
     // Capture and print out stats
     bool gen_stats;
 };