next - subsasgn doesn't promote correctly
Also, nan handling is not great. How can we get isnan working and nans handled properly?

@single overloaded methods
* asterisks marked completed routines
- minus marks unneeded (?) routines
? or space indicates ignorance of need

* abs
- strcmp
* acos
- strcmpi
* acosh
- strncmp
* all
- strncmpi
* and (?)
* sum   *** need to implement as mpfr_sum using mpfr_sum mpfr function
* any
? superiorfloat
* asin
  svd
* asinh
* tan
* atan
* tanh
* atan2
* times
* atanh
* transpose
  balance
* tril
* ceil
* triu
  chol
* uminus
  cholupdate
* uplus
* colon
- upper
* conj
- xor
  conv2
* cos
* cosh
* ctranspose
* cumprod
* cumsum
  det
  diag
  diff
* display
  eig
- eps
* eq
* exp
  expm
  fft
  fftn
  filter
* find
* fix
* floor
- full
* ge
* gt
  hess
  ifft
  ifftn
* imag
  inv
  isfinite
  isinf
- isletter
  isnan
- issorted
- isspace
  ldivide
* le
  linsolve
* log
* log2
- logical
- lower
* lt
* lu
* max
* min
* minus
  mldivide
  mod
* mpower
* mrdivide
* mtimes
* ne
* norm
* not
* or
  ordeig
  ordqz
  ordschur
- permute
* plus
  pow2
* power
* prod
* qr
  qrupdate
  qz
  rcond
* rdivide
* real
- reallog
- realpow
- realsqrt
* rem
- reshape
* round
  schur
* sign
* sin
* sinh
* sort
- sparsfun
* sqrt
