Add serde support for protobuf generated struct.

[jmjoy]

So protobuf generated struct can be serialized and deserialized.

[jmjoy]

There will be a new dependency serde_derive, it's under MIT OR Apache-2.0 license, so it's OK.

[codecov-commenter]

Codecov Report

Merging #35 (5f97bfd) into master (b5ac538) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #35   +/-   ##
=======================================
  Coverage   38.88%   38.88%           
=======================================
  Files          13       13           
  Lines         306      306           
=======================================
  Hits          119      119           
  Misses        187      187           

Impacted Files	Coverage Δ
src/skywalking_proto/v3/mod.rs	0.00% <ø> (ø)

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[wu-sheng]

Curious question, how we do serialization now?

[jmjoy]

Curious question, how we do serialization now?

The protobuf library use it's own trait prost::Message, not the most common serialize/deserialize library serde.

[wu-sheng]

I see. So, the serialization would change to use serde automatically after this change, we don't need explicitly calling the method, it is integrated into generated codes. Am I right?

[jmjoy]

I see. So, the serialization would change to use serde automatically after this change, we don't need explicitly calling the method, it is integrated into generated codes. Am I right?

Yes, for the serialization scenes which need serde.