Documentation added

README.md

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+# animatedsprite for SFML
+This is a (stupid) simple implementation of sprite animation for [SFML](https://www.sfml-dev.org/index.php). It contains two files:
+- animatedsprite.hpp
+- animatedsprite.cpp
+And those are all you need to get going. In the `test/` directory you find a super small program using the animatedsprite provided utlities.
+
+## The Animation File Format
+Animation files are just simple ASCII text files. See `test/testanimations.txt` as an example. Below the structure of each animation definition is described.
+
+Comment lines in the file start with `#` which are ignored, along with empty lines.
+
+Each animation starts with:
+`animation MyAnimationName`
+Followed by a collection of definition lines:
+- `frame-origin x y`
+  - Where `x` and `y` are unsigned integers.
+  - Where is the first sprite frame located in the spritesheet.
+- `frame-size x y`
+  - Where `x` and `y` are unsigned integers.
+  - How big is the sprite frame.
+- `frame-step x y`
+  - Where `x` and `y` are unsigned integers.
+  - How much the frame needs to be translated every new frame.
+  - Usually identical to your frame-size, but useful for example for  skipping every other frame.
+- `frame-margin x y`
+  - Where `x` and `y` are unsigned integers.
+  - Represents the "empty space" between frames. A lot of spritesheets come with empty space between each sprite frame. This is to prevent frames bleeding into each other.
+- `frame-count n`
+  - Where `n` is an unsigned integer.
+- `frame-time n`
+  - Where `n` is an unsigned integer and represents milliseconds.
+- `reverse`
+  - If present it reverse the animation.
+- `loop`
+  - If present it loops the animation by going back to the first frame after the last frame has been reached.
+- `bounce`
+  - If present it loops the animation by going in reverse whenever the last frame has been reached.
+
+The actual source code tells you most likely all you need to know:
+```cpp
+unsigned const x = frameOrigin.x + (frameNumber * frameMargin.x) + (frameNumber * frameStep.x);
+unsigned const y = frameOrigin.y + (frameNumber * frameMargin.y) + (frameNumber * frameStep.y);
+```
+Where x and y are the topleft coordinates of the sprite frame.