• document accepted inputs better
  
• fix wrong upgrade and undef-parameter handling in broot()
  
• implement broot() if lib doesn't have a _root() routine for $y that are
  powers of two and for small $x
  
• warn if broot() cannot yet compute proper result
  
• remove needless _one(): 3% speedup for binc()
  
• remove needless _swap(): 1% (Calc) - 6% (GMP) speedup for overloaded math