Add test for strings

test/asm/strings.s

+.text
+main:
+  la $a0, hello
+  li $v0, 1
+  syscall
+
+  la $a0, world
+  li $v0, 1
+  syscall
+
+  la $a0, hello
+  li $v0, 1
+  syscall
+
+  la $a0, hello
+  addi $a0, 8
+  li $v0, 1
+  syscall
+
+end:
+  li $v0, 10
+  syscall
+
+.data
+  hello: .asciiz "Hello"
+  world: .asciiz "World\n"