add CPU and memory modules with associated header files; update README and .gitignore

include/cpu.h

@@ -0,0 +1,29 @@
+#ifndef CPU_H
+#define CPU_H
+
+#include <stdint.h>
+
+typedef struct
+{
+    uint8_t A;  // accumulator
+    uint8_t X;  // index X
+    uint8_t Y;  // index y
+    uint8_t S;  // stack pointer
+    uint8_t PC; // program counter
+    uint8_t P;  // status flags
+} CPU6502;
+
+// status flag masks
+#define FLAG_C 0x01
+#define FLAG_Z 0x02
+#define FLAG_I 0x04
+#define FLAG_D 0x08
+#define FLAG_B 0x10
+#define FLAG_U 0x20
+#define FLAG_V 0x40
+#define FLAG_N 0x80
+
+void cpu_reset(CPU6502 *cpu);
+void cpu_print_state(CPU6502 *cpu);
+
+#endif