Fixed error when opening compressed wave files using ``from_wav`` or ``from_file(format='wav')``.
Added ".wave" extension alias.
Made ``utils.which`` work for windows systems, where executables have a ".exe" extension.
Removes warning for not finding ffmpeg or avconv even though they are installed for windows systems.
Merge branch 'master' of https://github.com/Benproductions1/pydub

Conflicts:
	pydub/utils.py
add no-ffmpeg, wave-only support back in.
Raise an exception when ffmpeg fails to decode an audio file