function filterConversions(conversions, typeNames) {
      var matches = {};

      conversions.forEach(function (conversion) {
        if (typeNames.indexOf(conversion.from) === -1 &&
            typeNames.indexOf(conversion.to) !== -1 &&
            !matches[conversion.from]) {
          matches[conversion.from] = conversion;
        }
      });

      return Object.keys(matches).map(function (from) {
        return matches[from];
      });
    }
Get params containing all types that can be converted to the defined types.

@param {ConversionDef[]} conversions
@param {string[]} typeNames
@return {ConversionDef[]} Returns the conversions that are available
                       for every type (if any)