feat: add functions and docs to conversions group

[42atomys]

Description

This pull request introduces three new functions toBool, toUint and toUint64 to the conversion group

Changes

• New functions: toBool, toUint and toUint64
• All conversion function are documented on https://docs.atom.codes/sprout

Fixes Masterminds/sprig#258, Masterminds/sprig#307

Checklist

• I have read the CONTRIBUTING.md document.
• My code follows the code style of this project.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have updated the documentation accordingly.
• This change requires a change to the documentation on the website.

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