* Refactored the way the library does validation: now we use
  github.com/go-playground/validator/v10 instead of custom ones.
* Now Parse() always return ValidationErrors containing one or more
  ValidationError if any validation error is present.
* The parser tries not to stop the validation early and give as many
  errors as possible immediately.
* The strict mode was removed
* The default output is now errorformat friendly
  (https://vim-jp.org/vimdoc-en/quickfix.html#error-file-format)
* pcvalidate learned the -json switch to ouput the report as JSON
* Specify the errored keys as a subset of JSONPath
  (fe. documentation.eng.features[3])

Fix italia#76, Fix italia#19, Fix italia#74, Fix italia#60.

Use the italia/publiccode-editor repository as we can change the
publiccode.yml more quickly, if we need to.

Related to italia#82.

* Remove -remote-base-url from the CLI.
  By default, files existence it's performed checking remotely
  using remote raw root URL, which is now autodetected from the publiccode.
  To check from the local directory use -path
* Similarly, the Go API now provides NewParser() and NewParserWithPath(),
  to use respectively the remote raw URL or a local path.

This allows for publiccode.yml to be in a different repository than the
one pointed by url and for absolute URLs in publiccode.yml to be
outside of the repository.

Related to italia/publiccode-crawler#85

Don't expand the relative path of files, the parser should
just deal with parsing and validation.

Disable checks that would most likely run into CORS errors when
running under WASM.