Introduced an example source file for all instructions

Provides calling conventions, ensures parser and lexer are working
correctly.  Will be updated as more instructions are introduced and
supported in the assembler.

examples/instruction-test.asm

@@ -0,0 +1,50 @@
+;;; instruction-test.asm: A file that contains all possible opcodes in
+;;; order, with proper calling convention.  Used to test lexer and
+;;; parser but isn't a semantically correct program, but may be run as
+;;; first instruction is halt (so program will stop immediately).
+  halt
+  push.byte 1
+  push.hword 2
+  push.word 3
+  pop.byte
+  pop.hword
+  pop.word
+  push-reg.byte 1
+  push-reg.hword 2
+  push-reg.word 3
+  mov.byte 1
+  mov.hword 2
+  mov.word 3
+  dup.byte 1
+  dup.hword 2
+  dup.word 3
+  not.byte
+  not.hword
+  not.word
+  or.byte
+  or.hword
+  or.word
+  and.byte
+  and.hword
+  and.word
+  xor.byte
+  xor.hword
+  xor.word
+  eq.byte
+  eq.hword
+  eq.word
+  plus.byte
+  plus.hword
+  plus.word
+  print.char
+  print.byte
+  print.int
+  print.hword
+  print.long
+  print.word
+  jump.abs 1
+  jump.stack
+  jump.register 2
+  jump.if.byte 1
+  jump.if.hword 2
+  jump.if.word 3