fix: resolve issues with the v0.6.0-rc.1

[42atomys]

Description

This pull requests grabs returns for the v0.6.0-rc.1 (Release Candidate 1) and resolve issues related to it.

Changes

• Add Raw prefix to Functions and Aliases function to be more comprehensible and prevent confusion with Funcs() from sprig.
• Remove deprecated NewFunctionhandler labelled as deprecated in v0.2.0 to prepare the v1.0.0
• Ensure a built function map cannot be rebuild and cause memory growing
• Prevent to creating an alias on a no-existant function name

Fixes #66, #67

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.

[codecov]

Codecov Report

Attention: Patch coverage is 95.34884% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
alias.go	80.0%	1 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
handler.go	100.0% <100.0%> (ø)
notice.go	100.0% <100.0%> (ø)
registry.go	100.0% <100.0%> (ø)
sprigin/sprig_backward_compatibility.go	100.0% <100.0%> (ø)
sprout.go	100.0% <100.0%> (ø)
alias.go	90.9% <80.0%> (-9.1%)	⬇️