v0.8.58

ApproxFunBase v0.8.58

Diff since v0.8.57

Merged pull requests:

• Delete AFOP test directory (#589) (@jishnub)
• isnegative in intpow (#590) (@jishnub)
• backport: isnegative in intpow (#591) (@jishnub)
• Don't treat ConstantOperator as a zeroop (#592) (@jishnub)
• Backport: Don't treat ConstantOperator as a zeroop (#593) (@jishnub)
• Restore skip CI (#594) (@jishnub)
• Implement calculus operations for ConstantSpace (#595) (@LucasAschenbach)
• Backport: Restore skip CI (#596) (@jishnub)
• Backport: Implement calculus operations for ConstantSpace (#597) (@jishnub)