Add support for defining custom methods

app/src/main/kotlin/io/smnp/callable/method/CustomMethod.kt

@@ -0,0 +1,42 @@
+package io.smnp.callable.method
+
+import io.smnp.callable.util.FunctionEnvironmentProvider
+import io.smnp.callable.util.FunctionSignatureParser
+import io.smnp.dsl.ast.model.node.FunctionDefinitionArgumentsNode
+import io.smnp.dsl.ast.model.node.FunctionDefinitionNode
+import io.smnp.dsl.ast.model.node.IdentifierNode
+import io.smnp.evaluation.evaluator.BlockEvaluator
+import io.smnp.evaluation.model.exception.Return
+import io.smnp.type.matcher.Matcher
+import io.smnp.type.model.Value
+
+object CustomMethod {
+    fun create(type: Matcher, objectIdentifier: String, node: FunctionDefinitionNode): Method {
+        val identifier = (node.identifier as IdentifierNode).token.rawValue
+
+        return object : Method(type, identifier) {
+            override fun define(new: MethodDefinitionTool) {
+                val (_, argumentsNode, bodyNode) = node
+                val signature = FunctionSignatureParser.parseSignature(argumentsNode as FunctionDefinitionArgumentsNode)
+                val evaluator = BlockEvaluator(dedicatedScope = false)
+
+                new method signature body { env, obj, args ->
+                    val boundArguments =
+                        FunctionEnvironmentProvider.provideEnvironment(argumentsNode, args, env).toMutableMap()
+                    boundArguments[objectIdentifier] = obj
+
+                    try {
+                        env.pushScope(boundArguments)
+                        evaluator.evaluate(bodyNode, env)
+                    } catch (value: Return) {
+                        return@body value.value
+                    } finally {
+                        env.popScope()
+                    }
+
+                    Value.void()
+                }
+            }
+        }
+    }
+}