Feature/validate

[nics]

Hi @nichtich I repackaged your validation code as a pull request.
I thinks this needs a little bit of cleanup and we want to release the current dev branch first to fix some filestore/multithreading related bugs.

[coveralls]

Coverage increased (+0.02%) to 94.499% when pulling ab0a068 on feature/validate into b7292bc on dev.

[nics]

hi @nichtich I removed the verbose option and made an issue to enhance the log fix (and others) to take the value of a field. That provides a more general solution:

   validate('author', MyValidatorClass, error_field: warnings)
   log($.warnings)

[nics]

Just realized there's already a long lingering issue #211 that proposes something similar.