Add ending frame position to static_sound

[cBournhonesque]

Here is my use case: https://github.com/tesselode/kira/issues/39 I'd like to have a single sound file and then arbitrary portions of them

I tried to make it such that start_position is inclusive and end_position is exclusive: if you define, start = 0.0, end = 1.0 then the frames will be [start, end[ (the frame corresponding to time 1.0 is end + 1)

[tesselode]

Hi, my apologies for never getting back to you on this. I did end up implementing this feature with a slightly different API for 0.8, but I appreciate the contribution regardless!