rewrite function for symbolic expressions

[burcin]

We should have a clean interface to various transformations one might want to perform on symbolic expressions. For example,

sage: rewrite(exp(x), "exp2sincos")
-I*sin(I*x) + cos(I*x)
sage: rewrite(exp(-I*x), "exp2sincos")
-I*sin(x) + cos(x)
sage: rewrite(exp(a+I*b), "exp2trig")
(sinh(a) + cosh(a))*(I*sin(b) + cos(b))
sage: rewrite((e^x)^2-e^(-2*x)+e^(-4*x)+(e^x)^4, 'exp2sinhcosh')
2*sinh(2*x) + 2*cosh(4*x)

The design of this interface is being fleshed out in

http://wiki.sagemath.org/symbolics/rewrite

See also http://docs.sympy.org/dev/modules/rewriting.html

CC: @rwst @mezzarobba

Component: symbolics

Issue created by migration from https://trac.sagemath.org/ticket/10137

[rwst]

Description changed:

--- 
+++ 
@@ -14,3 +14,5 @@
 The design of this interface is being fleshed out in
 
 http://wiki.sagemath.org/symbolics/rewrite
+
+See also http://docs.sympy.org/dev/modules/rewriting.html

[rwst]

comment:4

I think the first tangible step would be to provide a x.rewrite() with the same interface as SymPy's, calling SymPy. Later this can be adapted. However, I think the SymPy way is quite a good start.