mutable decl syntax change

examples/programs/conditional_unwrap/main.bro

@@ -6,10 +6,10 @@ observe func(counter @mut i32, value ?i32) ?i32 {
 }
 
 main func() i32 {
-	total i32 = 0
+	total i32 := 0
 
 	# present optional scalar -> binds v to the unwrapped value
-	a ?i32 = 40
+	a ?i32 := 40
 	if a |v| {
 		total = total + v          # 40
 	} else {
@@ -17,7 +17,7 @@ main func() i32 {
 	}
 
 	# null -> else branch taken; the binding is not in scope there
-	b ?i32 = null
+	b ?i32 := null
 	if b |v| {
 		total = total + v
 	} else {
@@ -25,20 +25,20 @@ main func() i32 {
 	}
 
 	# optional pointer present -> binds q to a non-null @i32; deref proves it
-	n i32 = 0
-	p ?@i32 = &n
+	n i32 := 0
+	p ?@i32 := &n
 	if p |q| {
 		total = total + q^         # +0
 	}
 
 	# optional pointer null -> skipped
-	z ?@i32 = null
+	z ?@i32 := null
 	if z |_| {
 		total = total + 1000
 	}
 
 	# guarded multi-unwrap exposes every capture to the guard and then-block
-	age ?i32 = 2
+	age ?i32 := 2
 	if a and age |value, years : value + years == 42| {
 		total = total
 	} else {
@@ -46,7 +46,7 @@ main func() i32 {
 	}
 
 	# parenthesized chains and three-value unwraps are equivalent
-	bonus ?i32 = 0
+	bonus ?i32 := 0
 	if (a and age and bonus) |value, years, extra : value + years + extra == 42| {
 		total = total
 	} else {
@@ -64,7 +64,7 @@ main func() i32 {
 	}
 
 	# a failed unwrap prevents later expressions from being evaluated
-	calls i32 = 0
+	calls i32 := 0
 	if b and observe(&calls, age) |missing, observed| {
 		total = total + missing + observed
 	}