release the mame core

I asked others and nobody minds. it's not like we're releasing a raw core that has accuracy or integration problems. it mostly works, and it's just modern mame with its current level of accuracy. if integration needs further tweaks to support more games, they will duly arrive while people use it for games that already work.

tasvideos used to only accept hawk submissions for cores marked as released in the code, which usually means the core author (or porter) considers it ready for business. I'm the original porter, and tasvideos staff, and I consider it generally ready. again, the other porter (CPP) didn't seem to mind.

src/BizHawk.Emulation.Cores/Arcades/MAME/MAME.cs

@@ -14,7 +14,7 @@
 
 namespace BizHawk.Emulation.Cores.Arcades.MAME
 {
-	[PortedCore(CoreNames.MAME, "MAMEDev", "0.250", "https://github.com/mamedev/mame.git", isReleased: false)]
+	[PortedCore(CoreNames.MAME, "MAMEDev", "0.250", "https://github.com/mamedev/mame.git", isReleased: true)]
 	public partial class MAME : IRomInfo
 	{
 		[CoreConstructor(VSystemID.Raw.Arcade)]