[Feature] customerized build script support

[shady831213]

Motivations: There always be some targets other than *.sv files need to be generated in the project. For example, some SDC files. And they should go with project and could be integrated or reused by other project.

Suggestion: Is it possible to provide some mechanism like build.rs in rust to support this? And I think build script and it's dependencies can also configurated in the toml file, just like rust. Thanks