Implement bisection algorithm in python according to the prescription below

use

def bis(f, x_m, x_p):
    ....
    return x0, f(x0)

-   make initial bracket for search, i.e. set $x_+$ and $x_-$ such that
    -   $f(x_+) >0$
    -   $f(x_-) <0$
-   loop begins
    -   make the new guess value $x_g=(x_+ + x_-)/2$
    -   if $|f(x_{g})| \le \varepsilon_f$ and $|x_{+}-x_{g}| \le  \varepsilon_x$\
        then stop, we found the solution with the desired precision
    -   otherwise if $f(x_{g})>0$ then $x_+=x_{g}$ else $x_-=x_{g}$
    -   continue the loop