Add `pop_back()`, `back()` and avoid `delete` in `erase()` method

src/Surfaces/SurfaceStack.cpp

@@ -9,8 +9,11 @@ void SurfaceStack::push_back(BaseSurface * s){
 	_surfaces.push_back(s);
 }
 
+void SurfaceStack::pop_back(){
+	_surfaces.pop_back();
+}
+
 void SurfaceStack::erase(int i){
-	delete _surfaces[i];
 	_surfaces.erase(_surfaces.begin() + i);
 }
 
@@ -35,5 +38,9 @@ BaseSurface * SurfaceStack::operator[](int i){
 	return _surfaces[i];
 }
 
+BaseSurface * SurfaceStack::back(){
+	return _surfaces.back();
+}
+
 } // namespace piMapper
 } // namespace ofx

src/Surfaces/SurfaceStack.h

@@ -12,6 +12,7 @@ class SurfaceStack {
 		SurfaceStack();
 
 		void push_back(BaseSurface * s);
+		void pop_back();
 		void erase(int i);
 		void swap(int a, int b);
 		void draw();
@@ -19,6 +20,7 @@ class SurfaceStack {
 		int size();
 
 		BaseSurface * operator[](int i);
+		BaseSurface * back();
 	
 	private:
 		vector<BaseSurface *> _surfaces;