Move from Jansson to JV - everything but the interpreter loop

Passes valgrind --leak-check=full.

c/compile.h

@@ -13,7 +13,7 @@ typedef struct block {
 
 block gen_noop();
 block gen_op_simple(opcode op);
-block gen_op_const(opcode op, json_t* constant);
+block gen_op_const(opcode op, jv constant);
 block gen_op_target(opcode op, block target);
 block gen_op_var_unbound(opcode op, const char* name);
 block gen_op_var_bound(opcode op, block binder);