creates missing directories when saving files

this handles every instance i can find. here's a minimal example that works now, whereas none of the files were saved before:

```c++
#include "ofAppGlutWindow.h"
#include "ofMain.h"

class ofApp : public ofBaseApp {
public:
	
	void setup() {		
		ofImage img;
		img.allocate(1, 1, OF_IMAGE_COLOR);
		img.saveImage("ofImage/out.png");
		
		ofFile file;
		file.open("ofFile/out.txt", ofFile::WriteOnly);
		file << "hello, world!";
		
		// uses ofFile
		ofSaveURLTo("https://www.google.com/", "ofSaveURLTo/out.html");
		
		// uses ofFile
		ofMesh mesh;
		mesh.save("ofMesh/out.ply");
		
		ofBeginSaveScreenAsPDF("ofBeginSaveScreenAsPDF/out.pdf");
		ofSetColor(0);
		ofCircle(100, 100, 50);
		ofEndSaveScreenAsPDF();
	}
	
	void update() {
	}
	
	void draw() {
	}
};

int main() {
	ofSetupOpenGL(1280, 720, OF_WINDOW);
	ofRunApp(ofPtr<ofBaseApp>(new ofApp()));
}
``` 

(note: ofSaveURLTo causes poco to crash on exit for some reason, but it's an unrelated bug)