Add documentation

- Add file documentation to about 1/4 of the files in Source
- Copy over a lot of the documentation from the sanctuary/notes repo
- Standardise all the existing documentation
- Create a configuration for Doxygen
- Add more documentation (engine.cpp is now fully documented)

Source/cursor.cpp

@@ -1,3 +1,8 @@
+/**
+ * @file cursor.cpp
+ *
+ * Implementation of cursor tracking functionality.
+ */
 #include "all.h"
 
 int cursH;
@@ -8,7 +13,7 @@ int icursW28;
 BYTE *pCursCels;
 int icursH;
 
-// inv_item value
+/** inv_item value */
 char pcursinvitem;
 int icursW;
 char pcursitem;
@@ -20,6 +25,7 @@ int pcurstemp;
 int pcurs;
 
 /* rdata */
+/** Maps from objcurs.cel frame number to frame width. */
 const int InvItemWidth[180] = {
 	// Cursors
 	0, 33, 32, 32, 32, 32, 32, 32, 32, 32, 32, 23,
@@ -43,6 +49,7 @@ const int InvItemWidth[180] = {
 	2 * 28, 2 * 28, 2 * 28, 2 * 28, 2 * 28, 2 * 28, 2 * 28, 2 * 28
 };
 
+/** Maps from objcurs.cel frame number to frame height. */
 const int InvItemHeight[180] = {
 	// Cursors
 	0, 29, 32, 32, 32, 32, 32, 32, 32, 32, 32, 35,