Missing complex tests/rules for scalar functions

[sethaxen]

Scalar functions with general rules but no complex tests:

• identity
• one
• zero
• deg2rad
• rad2deg
• abs2 (handled by Correct chainrules for abs2, abs, conj and angle #196)
• +
• -
• /
• \
• ^
• inv
• muladd
• sqrt
• sign (handled by Fix rules for sign with complex input #211)
• sincos
• exp2
• exp10
• expm1
• log
• log2
• log10
• log1p

Scalar functions defined/tested on reals that can be generalized to/tested on complex:

• real
• imag
• adjoint
• hypot
• exp
• abs (handled by Correct chainrules for abs2, abs, conj and angle #196)
• conj (handled by Correct chainrules for abs2, abs, conj and angle #196)
• angle (handled by Correct chainrules for abs2, abs, conj and angle #196)