doc: sample: add match-statement syntax and ir samples

doc/sample/Match.im

@@ -0,0 +1,18 @@
+
+age = 65.
+yz = 32.
+
+p3 = 3.
+
+q = match yz in
+	1 => do
+            wq = 32.
+            wq * 2
+        end,
+
+	2       => age / 12,
+	p3      => age / 365,
+        5 | 6   => age = 32,
+        10..=15 => age = 64,
+	_       => 0
+end

doc/sample/Match.mie

@@ -0,0 +1,47 @@
+define void @init() static {
+entry:
+	%age = alloca id
+	store i32 #65, ptr %age
+
+	%yz = alloca id
+	store i32 #32, ptr %yz
+
+	%p3 = alloca id
+	store i32 #3, ptr %p3
+
+	%1 = load id, ptr %yz
+	%2 = load id, ptr %p3
+
+	switch id %1, label %match.d,
+		[ i32 #1, label %match.0 ],
+		[ i32 #2, label %match.1 ],
+		[ i32 %2, label %match.2 ]
+match.0:
+	%wq = alloca id
+	store i32 #32, ptr %wq
+
+	%3 = load id, ptr %wq
+	%multmp = mul id %3, i32 #2
+	br label %match.end
+
+match.1:
+	%4 = load id, ptr %age
+	%divtmp = mul id %4, i32 #12
+	br label %match.end
+match.2:
+	%5 = load id, ptr %age
+	%divtmp.0 = mul id %5, i32 #365
+	br label %match.end
+match.d:
+	br label %match.end
+match.end:
+	%match.result = phi id
+		[ %match.0, %multmp],
+		[ %match.1, %divtmp ],
+		[ %match.2, %divtmp.0 ],
+		[ %match.d, #0 ]
+
+	%q = alloca id
+	store id %match.result, ptr %q
+	ret void
+}