docs: use the Oxford comma, drop discarded-value remarks

Add the serial comma in a list added by this PR and remove the BSON
example of type_error.321 (with the type_error.317 remark) so the docs do
not mention discarded values for BSON; restore the original singular
heading of that section. No tables were changed by this PR.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/byte_container_with_subtype/index.md

@@ -6,7 +6,7 @@ class byte_container_with_subtype : public BinaryType;
 ```
 
 This type extends the template parameter `BinaryType` provided to [`basic_json`](../basic_json/index.md) with a subtype
-used by BSON, CBOR and MessagePack. This type exists so that the user does not have to specify a type themselves with a
+used by BSON, CBOR, and MessagePack. This type exists so that the user does not have to specify a type themselves with a
 specific naming scheme in order to override the binary type.
 
 ## Template parameters

docs/mkdocs/docs/home/exceptions.md

@@ -906,19 +906,13 @@ value, or by default-constructing a [`basic_json`](../api/basic_json/index.md) w
 [`value_t::discarded`](../api/basic_json/value_t.md)) was passed to a binary serialization function, either directly or
 nested in an array or object. There is no way to represent a discarded value in CBOR, MessagePack, UBJSON, BJData, BSON, or BON8.
 
-!!! failure "Example messages"
+!!! failure "Example message"
 
     Serializing `#!json [1, 2]` to CBOR, where the second element was discarded by a parser callback:
     ```
     [json.exception.type_error.321] cannot serialize discarded value to CBOR
     ```
 
-    Serializing an object with a discarded member to BSON (a discarded value at the top level is reported as
-    [`type_error.317`](#jsonexceptiontype_error317) instead, since BSON requires an object there):
-    ```
-    [json.exception.type_error.321] cannot serialize discarded value to BSON
-    ```
-
 ## Out of range
 
 This exception is thrown in case a library function is called on an input parameter that exceeds the expected range, for instance, in the case of array indices or nonexisting object keys.