Bench:
- from Andreas Enge 9 June 2009:
  Scripts and web page comparing timings with different systems,
  as done for mpfr at http://www.mpfr.org/mpfr-2.4.0/timings.html

Efficiency:
- from Andreas Enge 16 September 2008:
  Once mpc_sin_cos exists, improve mpc_tan to use it

New functions to implement:
- from Andreas Enge 16 September 2008:
  mpc_sin_cos (needs mpfr_sinh_cosh)
- from Mickael Gastineau <gastineau@imcce.fr> 14 Apr 2008:
  mpc_fma: d=a*b+c
- from Andreas Enge and Philippe Théveny 17 July 2008
  agm (and complex logarithm with agm ?)
- from Andreas Enge 25 June 2009:
  correctly rounded roots of unity zeta_n^i

New tests to add:
- from Andreas Enge and Philippe Théveny 9 April 2008
  correct handling of Nan and infinities in the case of
  intermediate overflows while the result may fit (we need special code)
