Refactored validators.
fixed test break.
Fixed readme.
fixed markdown typo
Merge pull request #1451 from SebSept/patch-1

fixed markdown typo
Fixed safe validator.
Fixes #1454: refactored FileValidator.
Fixes #1457: support string representation of AR.
Fixes #1457: support using AR relations as input.
fixes #1427
Edited introduction.
Edited the first quarter
updated doc.
Merge pull request #4 from yiisoft/master

update from orig