Serialize to binary if the serde format is not human readable

This implements the KISS suggested in https://github.com/serde-rs/serde/issues/790.
It is possible that one of the other approaches may be better but this
seemed like the simplest one to reignite som discussion.

Personally I find the original suggestion of adding two traits perhaps slightly
cleaner in theory but I think it ends up more complicated in the end
since the added traits also need to be duplicated to to the `Seed`
traits.

Closes #790

serde_test/src/assert.rs

@@ -84,7 +84,17 @@ pub fn assert_ser_tokens<T>(value: &T, tokens: &[Token])
 where
     T: Serialize,
 {
-    let mut ser = Serializer::new(tokens);
+    assert_ser_tokens_readable(value, tokens, true)
+}
+
+/// Asserts that `value` serializes to the given `tokens`.
+///
+/// See: `assert_ser_tokens`
+pub fn assert_ser_tokens_readable<T>(value: &T, tokens: &[Token], human_readable: bool)
+where
+    T: Serialize,
+{
+    let mut ser = Serializer::readable(tokens, human_readable);
     match value.serialize(&mut ser) {
         Ok(_) => {}
         Err(err) => panic!("value failed to serialize: {}", err),
@@ -183,7 +193,14 @@ pub fn assert_de_tokens<'de, T>(value: &T, tokens: &'de [Token])
 where
     T: Deserialize<'de> + PartialEq + Debug,
 {
-    let mut de = Deserializer::new(tokens);
+    assert_de_tokens_readable(value, tokens, true)
+}
+
+pub fn assert_de_tokens_readable<'de, T>(value: &T, tokens: &'de [Token], human_readable: bool)
+where
+    T: Deserialize<'de> + PartialEq + Debug,
+{
+    let mut de = Deserializer::readable(tokens, human_readable);
     match T::deserialize(&mut de) {
         Ok(v) => assert_eq!(v, *value),
         Err(e) => panic!("tokens failed to deserialize: {}", e),