Add support for validation from metadata (e.g., annotations)

[ddeboer]

Add support for validation constraints from annotations (or other validation metadata sources).

Fix portphp/portphp#57.

[alexdruhet]

Hi, this is quite old PR but that lead to wrong behaviour since constraints are this way applied on the root object. Don't you think validator should be applied after object transformation/mapping?

[Baachi]

Hey @Pixadelic,

this depends strongly of your use case, this is why I introduced the step system. It allows you to configure your own workflow which fits your usecase. If you need to to validation after the mapping, just add the step after that.

[alexdruhet]

Hi @Baachi, thanks for your reply. It helps me to understand how I was wrong dealing with priority arguments in my workflow setup... It's clearer now.