Orthogonal collocation solver for two-point boundary value problems

@jstac @albop @spencerlyon2 @mmcky

I have implemented a generic solver that uses projection methods to solve systems of non-linear differential equations with boundary conditions.

Currently I have implemented collocation using orthogonal polynomials (typically Chebyshev) as basis functions. In near future (next week?) I will finish implementing a simple finite elements approach using B-splines as basis functions.

The orthogonal collocation solver is fast and accurate. But documentation is still lacking and I only have two (slightly messy) example notebooks that demonstrate how to use the solver: one for a Solow model and another for a Ramsey-Cass-Koopmans model. I am particularly keen to provide some microeconomic examples (perhaps auction models?) in addition to gathering more macro models (Romer growth model, search and match models, Tobin's q, credit-cycles, etc)

As always, feedback is much appreciated.

The issue names no repository files or tests, but mentions two existing example notebooks for Solow and Ramsey-Cass-Koopmans models. Start by reviewing those notebooks and the external bvp-solver project, then clarify whether the intended work is documentation, solver integration, or additional economic examples before defining what done means.