Implement 'character' literals (#1747)

test/asm/character-literals.asm

@@ -0,0 +1,34 @@
+def s equs "d"
+
+charmap "A", 1
+charmap "B", 2
+charmap "c{s}e", 3
+charmap "F", 4, 5, 6
+charmap "'", 42
+charmap "\"", 1234
+charmap "\n\r\t\0", 1337
+charmap "',\",\\", 99
+
+MACRO char
+	assert (\1) == (\2)
+ENDM
+
+char 'A', 1
+char 'B', 2
+char 'c{s}e', 3
+char '\'', 42
+char '"', 1234
+char '\n\r\t\0', 1337
+char '\',",\\', 99
+
+char charval("c{s}e", 0), 'c{s}e'
+
+def v equs "\n\r\t\0"
+def x = '{v}'
+char x, '\n\r\t\0'
+
+; errors
+char '?', $3f ; ASCII
+char 'F', 0
+char 'ABF', 0
+char '\n\r\t', 0