Restructure build workflow

* All segments are now extracted from the base ROM; the base ROM is no
longer a compile time dependency
* ROM segments are now positioned relatively to each rather than with
hard coded addresses
* Piracy checksums are calculated during build

src/romheader/romheader.s

@@ -0,0 +1,35 @@
+.data
+
+.set VERSION_NTSC_BETA,  0
+.set VERSION_NTSC_1_0,   1
+.set VERSION_NTSC_FINAL, 2
+.set VERSION_PAL_BETA,   3
+.set VERSION_PAL_FINAL,  4
+.set VERSION_JAP_FINAL,  5
+
+
+.word 0x80371240 # Identifier
+.word 0x0000000F # Clock rate
+.word 0x80001000 # Program counter
+.word 0x00001449 # Release address
+.word 0x00000000 # CRC 1
+.word 0x00000000 # CRC 2
+.word 0x00000000
+.word 0x00000000
+
+.ascii "Perfect Dark        "
+.word 0x00000000
+.byte 0x00
+.byte 0x00
+.byte 0x00
+.ascii "NPDE"
+
+# Version
+.if VERSION == VERSION_NTSC_BETA
+	.byte 0x01
+.elseif VERSION == VERSION_NTSC_FINAL
+	.byte 0x01
+.else
+	.byte 0x00
+.endif
+