add TR14, TR15, TR16, as_trig

TR14 converts factored identity expressions to simpler forms

TR15 and TR16 are similar to TR5 and TR6 except that they work with
  inverse powers of sin and cos, like 1/cos(x)**2

as_trig converts an expression's hyperbolics to trig functions using
Osborne's rule after masking off pre-existing trig functions.