Adds the boolean attributes to checkbox and textarea helper methods.

[jwoertink]

Purpose

Fixes #952

Description

Adds the ability to set boolean attributes attrs: [:required] on textarea and checkbox methods.

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test

[paulcsmith]

Thanks for fixing this :D Just one suggestion for keeping duplication down

[paulcsmith]

Looks good!