Prevent system sleep while streaming

[nmaier]

While streaming, prevent the system from going into full sleep mode. Streaming in this context might mean a couple of things, tho:

• While a client is actually served
• Grace period afterwards (because the client might buffer a lot, and because this gives the user a chance to select next item after the current one finishes)

Platforms

• Windows: https://msdn.microsoft.com/en-us/library/aa373208%28v=vs.85%29.aspx
• OSX: http://stackoverflow.com/q/5596319/484441
• Linux: ? No sane solution
• iOS/Android: Don't care
• Other *nix/BSD: ?