Reduce the duplicated code

The grammar has been shorted removing duplicated or very similar elements
(for example method definitions are now function definitions).
By doing this, it gets simplier in all aspects since the code gets
centralized.

src/main/java/com/ruke/vrjassc/translator/expression/FunctionDefinition.java

@@ -2,6 +2,7 @@
 
 import java.util.Collection;
 
+import com.ruke.vrjassc.vrjassc.symbol.ClassSymbol;
 import com.ruke.vrjassc.vrjassc.symbol.FunctionSymbol;
 import com.ruke.vrjassc.vrjassc.symbol.MethodSymbol;
 import com.ruke.vrjassc.vrjassc.symbol.Modifier;
@@ -25,7 +26,7 @@ public String translate() {
 
 			this.expressions.clear();
 
-			if (this.function instanceof MethodSymbol) {
+			if (this.function.getParentScope() instanceof ClassSymbol) {
 				if (!this.function.hasModifier(Modifier.STATIC)) {
 					this.add(new RawExpression("integer this"));
 				}

src/main/java/com/ruke/vrjassc/translator/expression/VariableStatement.java

@@ -1,8 +1,8 @@
 package com.ruke.vrjassc.translator.expression;
 
 import com.ruke.vrjassc.vrjassc.symbol.LocalVariableSymbol;
+import com.ruke.vrjassc.vrjassc.symbol.Modifier;
 import com.ruke.vrjassc.vrjassc.symbol.Symbol;
-import com.ruke.vrjassc.vrjassc.symbol.Type;
 import com.ruke.vrjassc.vrjassc.util.Prefix;
 import com.ruke.vrjassc.vrjassc.util.VariableTypeDetector;
 
@@ -40,7 +40,7 @@ public String translate() {
 
 		String result = type + " " + name;
 
-		if (this.variable instanceof LocalVariableSymbol) {
+		if (this.variable.hasModifier(Modifier.LOCAL)) {
 			result = "local " + result;
 		}