allow non null-terminated strings in gl.Strs

This change allows non null-terminated strings to be passed as parameters
to gl.Strs. The original motivation for not allowing such was that it was
not useful, however we have recently discovered that gl.ShaderSource and
probably a few other functions take a `lengths` parameter whereby they do
not strictly need a null-terminated string.

Since go-gl/gl and go-gl/glow are low-level libraries that mimic the C
API, we relax this restriction and document the behavior users can expect.

Fixes go-gl/gl#46

tmpl/conversions.tmpl

@@ -65,13 +65,13 @@ func GoStr(cstr *uint8) string {
 	return C.GoString((*C.char)(unsafe.Pointer(cstr)))
 }
 
-// Strs takes a list of null-terminated Go strings and return's their C counterpart.
+// Strs takes a list of Go strings (with or without null-termination) and
+// returns their C counterpart.
 //
-// The returned free function must be called once you are done using the strings in
-// order to free the memory.
+// The returned free function must be called once you are done using the strings
+// in order to free the memory.
 //
-// If no strings are provided as a parameter, or if any string is not null-terminated,
-// this function will panic.
+// If no strings are provided as a parameter this function will panic.
 func Strs(strs ...string) (cstrs **uint8, free func()) {
 	if len(strs) == 0 {
 		panic("Strs: expected at least 1 string")
@@ -80,9 +80,6 @@ func Strs(strs ...string) (cstrs **uint8, free func()) {
 	// Allocate a contiguous array large enough to hold all the strings' contents.
 	n := 0
 	for i := range strs {
-		if !strings.HasSuffix(strs[i], "\x00") {
-			panic("Strs: str argument missing null terminator: " + strs[i])
-		}
 		n += len(strs[i])
 	}
 	data := C.malloc(C.size_t(n))