Smarter Scandoubler

[sy2002]

We need to make our Scandoubler smarter. Right now, several parameters are hardcoded, for example but not limited to video_mixer's input parameters:

	parameter LINE_LENGTH  = 768,
	parameter HALF_DEPTH   = 0,
	parameter GAMMA        = 0

This can lead to problems such as wrong colors or some cores not even working on certain monitors. For example for @sho3string the scan doubled mode of Galaga is not working on his analog ("VGA") monitor, while for @sy2002 it is.

Here is a copy/paste from a Skype chat between sy2002 and @sho3string:

1. Galaga via analog out ("VGA") using all three modes "Standard", "15 kHz HS/VS" and "15 kHz CSync" all work like a charme on my monitor. I am talking about the release version that you've put on the filehost.
2. The same is true for Xevious : Works perfect in all three VGA modes
3. But Bosconian has color glitches in "Standard" VGA mode (it is "too pink") but it works fine in 15 Khz HS/VS and in CSYNC mode.
4. Please send me Bomb Jack. Maybe VS/HS works on my Monitor.

What this is showing me: The raw analog output of these Arcade cores need some better processing to work on all analog ("VGA") monitors. Our standard M2M scandoubler is not always catching the right RGB info and therefore timing, this is why Bosconian is too pink in scandoubled mode (aka "Standard") but works fine in 15 kHz mode (HS/VS or CSYNC).