ResearchTools integration

[itaybthl]

Though it's been decided that the two codebases should remain separate, we have decided that the continued fraction calculator should be shared between the two, taking over the existing PCF of ResearchTools.

Migrate lib/pcf.py to ResearchTools, merging the two PCF files and PCF classes. In case of conflicting definitions, or duplicate features, prioritize LIReC's API and performance. Ensure that:

• The end result has all features of both.
• All code within LIReC refers to the (new) ResearchTools PCF class.
• All code within ResearchTools that uses the PCF class still functions as expected.

This issue contains a few smaller, secondary objectives, to be done after the main issue is resolved:

1. Migrate pcf_from_matrix to a static method of PCF.
2. Add a similar static method that converts SICFs to PCFs, either by upgrading pcf_from_matrix or adding a new from_sicf method. This should allow for both of $a_n,b_n$ to be cyclic sequences of polynomials, and not just $a_n$.
3. Add a generalized version of pcf_from_matrix that converts any 2x2 matrix of lambdas (or sympy expressions) to a GCF.