Put rule classes in their own files

src/rules/choice.cpp

@@ -0,0 +1,30 @@
+#include "choice.h"
+#include "transition_map.h"
+
+namespace tree_sitter  {
+    namespace rules {
+        Choice::Choice(const Rule &left, const Rule &right) : left(left.copy()), right(right.copy()) {};
+        Choice::Choice(rule_ptr left, rule_ptr right) : left(left), right(right) {};
+        
+        TransitionMap<Rule> Choice::transitions() const {
+            auto result = left->transitions();
+            result.merge(right->transitions(), [&](rule_ptr left, rule_ptr right) -> rule_ptr {
+                return rule_ptr(new Choice(left, right));
+            });
+            return result;
+        }
+
+        bool Choice::operator==(const Rule &rule) const {
+            const Choice *other = dynamic_cast<const Choice *>(&rule);
+            return (other != NULL) && (*other->left == *left) && (*other->right == *right);
+        }
+
+        Choice * Choice::copy() const {
+            return new Choice(left, right);
+        }
+        
+        std::string Choice::to_string() const {
+            return std::string("(choice ") + left->to_string() + " " + right->to_string() + ")";
+        }
+    }
+}