New decorators

What's Changed

• feat: IsHexadecimal decorator + test + readme by @maplecfiv in #16
• feat: IsURL decorator + test + readme by @maplecfiv in #17
• feat: IsHalfWidth decorator + test + readme by @maplecfiv in #18
• feat: IsFullWidth decorator + test + readme by @maplecfiv in #19

Full Changelog: 0.7.6...0.7.7