main: add tests

Add testing infrastructure and one initial test (for
src/runtime/print.go). More tests to be added later.

testdata/print.go

@@ -0,0 +1,39 @@
+package main
+
+func main() {
+	// test basic printing
+	println("hello world!")
+	println(42)
+	println(100000000)
+
+	// check that this one doesn't print an extra space between args
+	print("a", "b", "c")
+	println()
+	// ..but this one does
+	println("a", "b", "c")
+
+	// print integers
+	println(uint8(123))
+	println(int8(123))
+	println(int8(-123))
+	println(uint16(12345))
+	println(int16(12345))
+	println(int16(-12345))
+	println(uint32(12345678))
+	println(int32(12345678))
+	println(int32(-12345678))
+	println(uint64(123456789012))
+	println(int64(123456789012))
+	println(int64(-123456789012))
+
+	// print float64
+	println(3.14)
+
+	// print map
+	println(map[string]int{"three": 3, "five": 5})
+
+	// TODO: print pointer
+
+	// print bool
+	println(true, false)
+}

testdata/print.txt

@@ -0,0 +1,20 @@
+hello world!
+42
+100000000
+abc
+a b c
+123
+123
+-123
+12345
+12345
+-12345
+12345678
+12345678
+-12345678
+123456789012
+123456789012
+-123456789012
++3.140000e+000
+map[2]
+true false