Add KDoc comment in generated code

[sh-cho]

Motivation

Comments in proto are not included in generated code

Modification

• Adds KDoc using SourceCodeInfo
• Update README.md about available options (quite confusing currently)
• Update generated-code-tests

Result

• Resolves Add in-code comments to generated code #6
• Add option generate_comments (default: false)

[Dogacel]

Hi @sh-cho , I see you have 2 PRs now. Do you use kotlinx-protobuf-gen in production?

[sh-cho]

@Dogacel Unfortunately no, I'm trying to use it in personal project

[Dogacel]

@Dogacel Unfortunately no, I'm trying to use it in personal project

I'm quite busy nowadays and I haven't used this library for some time, I will take a look once I have some spare time. Let me know if it ha any urgency.

[sh-cho]

@Dogacel I'm not in hurry. These are just enhancements. Take your time :)