WIP: Specs for continued fraction algorithms

[sr-murthy]

[WORK IN PROGRESS]

Adds TLA specs for:

1. Core algorithm for finding the (unique) simple continued fraction of a rational number based on Euclidean division.
2. Algorithm for constructing a rational number from the sequence of coefficients of a simple continued fraction.
3. Algorithm for finding the k-th convergent of a simple continued fraction.
4. Algorithm for finding the k-th remainder of a simple continued fraction.
5. Algorithm for finding the semiconvergent of two consecutive convergents of a simple continued fraction.

[sr-murthy]

Have to redo this, because of some GitHub issues.