use string interpolation when logging, makes the message easier to read
don't send Transfer-Encoding HTTP header, it doesn't seem to be
helping at all
[squash] to log message
use pipe:1 instead of "-" to send output to stdout (this seems to be
the standard way of doing that)
use the avconv package for spawning avconv, it contains some useful
wrappers that we want/need
bump version to 0.2