Add simplifications for number conversions

[jfmengels]

Fixes #259

• toFloat 1 -> 1
• round 1 -> 1
• ceiling 1 -> 1
• floor 1 -> 1
• truncate 1 -> 1

Compositions of these functions:

• round << toFloat -> identity
• ceiling << toFloat -> identity
• floor << toFloat -> identity
• truncate << toFloat -> identity

[jfmengels]

All great suggestions, thank you :+1: