Fix the consistency of name validity between Haskell and Rust.

[td202]

Purpose

Backport of #561.

Fix the consistency of how contract init, receive and entrypoint names are handled between Haskell and Rust.
Changes

Changes

• Broaden what is accepted in Haskell to match what is accepted in Rust.-
• Additional test in Rust and Haskell.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[td202]

Closed as #561 was merged.