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.