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 https://github.com/Masterminds/sprig/issues/258, https://github.com/Masterminds/sprig/pull/307

Checklist

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

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