refactor: compose division ops for ContinuedFraction

[sr-murthy]

All division operations in ContinuedFraction:

• continuedfraction.ContinuedFraction.__truediv__
• continuedfraction.ContinuedFraction.__rtruediv__
• continuedfraction.ContinuedFraction.__floordiv__
• continuedfraction.ContinuedFraction.__rfloordiv__

can be refactored by composing the division-free algorithms for the negation and inversion of simple continued fractions of positive rational numbers, which are described in the documentation.

A new __invert__ operation is required for the composition, which implements the following algorithm for the inversion of a positive rational number $\frac{a}{b}$ with simple continued fraction $[a_0;a_1,\dots ,a_n]$: the positive inversion $+\frac{b}{a}$ is given by:

$$+\frac{b}{a}=\{\begin{array}{ll}[a_1;a_2,\dots ,a_n],& \text{if }0<a<b⟺a_0=0\\ [0;a_0,a_1,\dots ,a_n],& \text{if }0<b<a⟺a_0\ge 1\end{array}$$

and the negative inversion $-\frac{b}{a}$ is given by:

$$-\frac{b}{a}=\frac{1}{-\frac{a}{b}}=-\left(\frac{1}{\frac{a}{b}}\right)=\{\begin{array}{ll}[-1;a_0-1],& n=0\text{ and }{a}_0\ge 1\\ [-1;1,a_0-1,2],& n=1\text{ and }{a}_0\ge 2\\ [-1;2,a_2,\dots ,a_n],& n\ge 2\text{ and }{a}_0=1\\ [-1;1,a_0-1,1,a_2,\dots ,a_n],& n\ge 2\text{ and }{a}_0>1\end{array}$$

In applying this algorithm there is an assumption that the last element $a_n>1$, as any simple continued fraction of type $[a_0;a_1,\dots ,a_n=1]$ can be reduced to the simple continued fraction $[a_0;a_1,\dots ,a_{n-1}+1]$.