Improved build process to enable more options to be specified

Makefile

@@ -1,11 +1,23 @@
 BEEBASM?=beebasm
 PYTHON?=python
 
-.PHONY:build
-build:
+# A make command with no arguments will build Aviator with crc32
+# verification of the game binaries
+#
+# Optional arguments for the make command are:
+#
+#   verify=no           Disable crc32 verification of the game binaries
+#
+# So, for example:
+#
+#   make verify=no
+#
+# will build Aviator with no crc32 verification
+
+.PHONY:all
+all:
 	$(BEEBASM) -i 1-source-files/main-sources/aviator-source.asm -v > 3-assembled-output/compile.txt
 	$(BEEBASM) -i 1-source-files/main-sources/aviator-disc.asm -do 5-compiled-game-discs/aviator-bbcmicro-co-uk.ssd -opt 3 -title "Aviator"
-
-.PHONY:verify
-verify:
+ifneq ($(verify), no)
 	@$(PYTHON) 2-build-files/crc32.py 4-reference-binaries/bbcmicro-co-uk 3-assembled-output
+endif