Golang library for validating package against specs

[ycombinator]

This PR is replaced by #10.

This PR creates a go module that provides an API for validating a package against the appropriate specification version. The API is as follows:

import "github.com/elastic/package-spec/code/go/pkg/validator"

validationErrs := validator.ValidateFromPath("/path/to/package/root/folder")

where validationErrs will implement the error interface type.

Resolves #4.

Author TODO

• Implement scaffolding
• Implement folder structure validation
• Implement file content validation

[ycombinator]

Replaced by #10.