bump version to 0.5.0

libwebp{,decoder} - 0.5.0
libwebp libtool - 6.0.0
libwebpdecoder libtool - 2.0.0

mux/demux - 0.3.0
libtool - 2.0.0

Change-Id: I5346d13eb827fb5890efbb63ff3f28cea9d0c55f
10 files changed