Functions `deserialize` and `deserialize_from` are confusing

[dtolnay]

It sounds like we picked two different names for the same thing and randomly allocated one to each signature. Both functions are deserializing from something.

[TyOverby]

deserialize_slice and deserialize_from_reader?

Same argument applies to the encoding APIs as well

[dtolnay]

The Rust convention is from_xyz.

• str::from_utf8 - the input is UTF-8 bytes that should be interpreted as a str.
• slice::from_raw_parts - the input is raw parts that should be interpreted as a slice.
• serde_json::from_str - the input is a str that should be interpreted as JSON.