Add props as extra argument to validators.

[ghedsouza]

This is a proposed WIP change to add props as a third argument to validators. It is a fix for #17.

This change allows you to depend on the props that redux-form passes along to the validate prop.

e.g.

return createValidator(
    message => (value, allValues, props) => {
      if (!allValues || value !== allValues[otherField] || props.forceFail) {
        return message;
      }
    },

    field => `${field} must match ${otherFieldLabel}`
  );

Still TODO:

1. Update createValidatorWithMultipleErrors.js.
2. Update tests.

Looking for feedback from the project maintainer before continuing work on this.

[codecov-io]

Codecov Report

Merging #60 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #60   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          30     30           
  Lines         225    225           
  Branches       62     62           
=====================================
  Hits          225    225

Impacted Files	Coverage Δ
src/createValidator.js	100% <100%> (ø)	⬆️
src/internal/internalCombineValidators.js	100% <100%> (ø)	⬆️
src/internal/createValidatorWithSingleError.js	100% <100%> (ø)	⬆️

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