Add playback speed 1.5x

[ORelio]

Hi,

Thanks for your hard work on pplay, the app works nicely 👍

I often watch shows at 1.5x speed and missed the feature on pplay, so here is a small contribution to add it. Basically, all it does is adding 1.5x between 1.0x and 2.0x playback speeds. I have not been able to recompile the project due to all the dependencies it requires but I'm fairly confident the change is valid C++ and should work just well. Looking forward to seeing it included in the next release :)

[ORelio]

@Cpasjuste It seems like you are not interested in this pull request since you handled other pull requests and made change to the repository but did not bother to respond here; so I'll close it now.

Just in case, here is the relevant diff for player.cpp:

@@ -277,7 +277,15 @@ bool Player::onInput(c2d::Input::Player *players) {
    if (keys & c2d::Input::Key::Fire5) {
        setSpeed(1);
    } else if (keys & c2d::Input::Key::Fire6) {
-        double new_speed = mpv->getSpeed() * 2;
+        double old_speed = mpv->getSpeed();
+        double new_speed = old_speed;
+        if (old_speed < 1.4) {
+            new_speed = 1.5;
+        } else if (old_speed < 1.9) {
+            new_speed = 2;
+        } else {
+            new_speed = old_speed * 2;
+        }
        if (new_speed <= 100) {
            setSpeed(new_speed);
        }