Transform complex exponentials into sin and cos : sincos exp2trig

### 2.21.12 Transform complex exponentials into sin and cos : `sincos exp2trig`

`sincos` or `exp2trig` takes as argument an expression containing complex exponentials.
`sincos` or `exp2trig` rewrites this expression in terms of sin and cos.
Input :

`sincos(exp(i*x))`

Output :

`cos(x)+(i)*sin(x)`

Input :

`exp2trig(exp(-i*x))`

Output :

`cos(x)+(i)*(-(sin(x)))`

Input :

`simplify(sincos(((i)*(exp((i)*x))```^```2-i)/(2*exp((i)*x))))`

Or :

`simplify(exp2trig(((i)*(exp((i)*x))```^```2-i)/(2*exp((i)*x))))`

Output :

`-sin(x)`