Lua: more Lua-ish function naming

[hryx]

song:play(true) and song:play(false) are so named because that's how the C API looks. But Lua scripts typically look a little friendlier. These should be renamed to song:play() and song:stop().

[hryx]

In the future, we should keep our eyes open for other cases where this could apply. Setting tempo is probably a common task, so song:setTempo(120) would be nicer than song:effectCommand(0, 17, 120). THINK OF THE CHILDREN