Bump version to 0.4.
Bump version to 0.4.

divanovGH/voluptuous,SimplyKnownAsG/voluptuous,tuukkamustonen/voluptuous,jmwri/voluptuous,natlownes/voluptuous,alecthomas/voluptuous,SimplyKnownAsG/voluptuous,tuukkamustonen/voluptuous,artburkart/voluptuous,alecthomas/voluptuous