Support 'MACRO mac' as well as 'mac: MACRO' for defining macros

The new syntax is used in documentation, but
the old syntax is not yet deprecated.

test/asm/macro-syntax.asm

@@ -0,0 +1,15 @@
+
+	old: MACRO ; comment
+		println "out with the ", \1
+	ENDM ; comment
+
+	MACRO new ; comment
+		println "in with the ", \1
+	ENDM ; comment
+
+	old 1
+	new 2
+
+	bad1: MACRO bad2 ; comment
+		println "which?"
+	ENDM ; comment

test/asm/macro-syntax.err

@@ -0,0 +1,5 @@
+ERROR: macro-syntax.asm(13):
+    syntax error, unexpected identifier, expecting newline
+ERROR: macro-syntax.asm(15):
+    syntax error, unexpected ENDM
+error: Assembly aborted (2 errors)!

test/asm/macro-syntax.out

@@ -0,0 +1,3 @@
+out with the $1
+in with the $2
+which?

test/asm/macro-syntax.simple.err

@@ -0,0 +1,5 @@
+ERROR: macro-syntax.asm(13):
+    syntax error
+ERROR: macro-syntax.asm(15):
+    syntax error
+error: Assembly aborted (2 errors)!