Add config file parsing and add option to set default encoding
frame size.

Config file is in /etc/enigma2/streamproxy.sh, options are like:
listen = 8002:transcode

Both command line and config file options are honoured, command
line options take precedence.

The new option --size sets the default frame size. In a future
commit, a client will be able to request a frame size on a per
session base, but first implement a default value. The value can
be either 480p, 576p and 720p. This can be given as "--size ..."
or it can be set in the config file as "size = ....".
Replace vlog and snprintf by generic logging and conversion module.
Add various encoding options, they can be set as default using
command line parameters, but also introduce a config file
(/etc/enigma2/streamproxy.conf) that holds default values for
encoding parameters. Besides that, the parameters can be
adjusted on a per-stream basis using url parameters.

Options:
-f [ --foreground ]   run in foreground (don't become a daemon)
-g [ --group ] arg    require streaming users to be member of this group
-l [ --listen ] arg   listen to tcp port with default action
-s [ --size ] arg     default transcoding frame size (480p (default), 576p or 720p)
-b [ --bitrate ] arg  default transcoding bit rate (100 - 10000 kbps)(default 1000)
-P [ --profile ] arg  default transcoding h264 profile (baseline (default), main, high)
-L [ --level ] arg    default transcoding h264 level (3.1 (default), 3.2, 4.0)
-B [ --bframes ] arg  default transcoding h264 b frames (0 (default), 1 or 2)

Config file:
listen = 8002:transcode
listen = 8003:transcode
size = 480p
bitrate = 1000
profile = baseline
level = 3.1
bframes = 0

Url:
http://..?..&size=480p
http://..?..&bitrate=1000
http://..?..&profile=baseline
http://..?..&level=3.1
http://..?..&bframes=0

Please note that these are the only safe properties/values to use. All other
values will make the transcoding engine crash. Streamproxy will therefore
not honour other values than advertised in the usage message.