Updated chtdb.txt and added new types F5, 52 & 53. Cleaned up type 51

Chtdb.txt
=========
Updated the header to document all the new cheat types, added some more cheats
and cleaned up others.

New Cheat Types:-
=================
F5 - 16-Bit toggle cheat, predominatly used with the D7 cheat to enable/disable
      ASM cheats with the same key presses. See chtdb.txt for more information.

52 - Register Block Conditionals for use with the type 51 cheats. There are 128 
      sub types. See chtdb.txt for more information.
      
53 - Improved Slide Code cheat type, with support for 65536 addresses and a 16
      bit step and easily configurable step direction for value and address.
      See chtdb.txt for more information.      

Other Changes:-
===============
51 - Cleaned up - renumbered/renamed, Tested & Bugfixed. See chtdb.txt for more 
      information.

src/core/cheats.h

@@ -45,6 +45,7 @@ struct CheatCode
     CompareGreater8 = 0xE3,
     Slide = 0x50,
     MemoryCopy = 0xC2,
+    ExtImprovedSlide = 0x53,
 
     // Extension opcodes, not present on original GameShark.
     ExtConstantWrite32 = 0x90,
@@ -63,6 +64,8 @@ struct CheatCode
     ExtConstantForceRangeRollRound16 = 0xF2,
     ExtConstantForceRange16 = 0xF3,
     ExtFindAndReplace = 0xF4,
+    ExtConstantSwap16 = 0xF5,
+
     ExtConstantBitSet8 = 0x31,
     ExtConstantBitClear8 = 0x32,
     ExtConstantBitSet16 = 0x81,
@@ -76,7 +79,8 @@ struct CheatCode
     ExtSkipIfNotLess16 = 0xC5,
     ExtSkipIfNotGreater16 = 0xC6,
 
-    ExtTempVariable = 0x51,
+    ExtCheatRegisters = 0x51,
+    ExtCheatRegistersCompare = 0x52,
   };
 
   union Instruction