added boolean rule

Merge pull request rakit#125 from kidstell/CaptureIntegersOnSizeTrait

Improve SizeTraits for Integers - Closes rakit#85

added explanation about size rule with/without numeric rule

Merge pull request rakit#115 from ashuradev/feature/nullable-rule

Add nullable rule

fix TypeError in ArrayUnset, support root asterisk, and declare error…

…s attribute

Fix return type Attribute::getValue

Added alpha_spaces and extension rules

Fix readme sample unique rule

added mime type audio/mp3 to validate mp3 file