patterns: More accurate variable declarations on nes.hexpat, add n64, gen, and gbx.hexpat (#477)

* Add n64, gen, and gbx.hexpat

* Add n64, gbx, and gen.hexpat to README.md

* Remove leftover string import from n64.hexpat

* More accurate variable declarations on nes.hexpat

* Add source to gbx.hexpat

* Add accidentally missing curly brace in nes.hexpat

patterns/gbx.hexpat

@@ -0,0 +1,61 @@
+#pragma author gmestanley
+#pragma description GameBoy ROM file GBX footer
+#pragma source hhug.me/gbx/1.0
+
+import gb;
+
+bitfield SachenMMC2SolderPad {
+	padding : 5;
+	opt1 : 1;
+	openBus512KiBOuterBanks : 1;
+	openBus1MiBOuterBanks : 1;
+};
+
+bitfield VastFameRunningValueType {
+	TaiwanReleases : 1;
+	MainlandChinaReleases : 1;
+};
+
+enum VastFamePCBType : u8 {
+	DSHGGB81,
+	BCR1616T3P
+};
+
+fn specialMapper(str value) { return value == "SAM2" || value == "VF01" || value == "GB81"; };
+
+struct MapperVariables {
+	match(parent.mapper) {
+		("SAM2"): SachenMMC2SolderPad solderPadConfig;
+		("VF01"): VastFameRunningValueType runningValue;
+		("GB81"): VastFamePCBType pcb; }
+	padding[3*specialMapper(parent.mapper)];
+	u32 mapperVariables[8-specialMapper(parent.mapper)];
+};
+
+struct CartridgeInformation {
+	char mapper[4];
+	bool battery;
+	bool rumble;
+	bool timer;
+	padding[1];
+	u32 romSize;
+	u32 ramSize;
+	if (specialMapper(mapper))
+		MapperVariables mapperVariables;
+	else
+		MapperVariables mapperVariables [[inline]];
+};
+
+struct GBXMetadata {
+	u32 footerSize;
+	u32 majorVersion;
+	u32 minorVersion;
+	char signature[4];
+};
+
+struct GBXFooter {
+	CartridgeInformation cartInfo;
+	GBXMetadata metadata;
+};
+
+be GBXFooter gbxFooter @ std::mem::size() - 0x40;