Add additional reverse contractors

[mewilhel]

Add support for the following contractors:

• [ ] erf
• [ ] erfc
• [ ] erfinv
• [ ] erfcinv
• [ ] sign
• [ ] abs2
• [ ] atan (2-argument form; formerly atan2)
• [ ] sec
• [ ] csc
• [ ] cot
• [ ] asec
• [ ] acsc
• [ ] acot
• [ ] csch
• [ ] sech
• [ ] coth
• [ ] csch
• [ ] sech
• [ ] coth

Potentially scaled versions of trignometric functions as well.