v0.8.8: Bug fixes for extracting the stability of solutions

• fixed bug where the plotting method ODESystem.plot_continuation would throw an error when PAR(14) was used as the time parameter for the x-axis
• fixed bug where the merging of branches caused the wrong diagnostic files to be pulled up for determining the solution stability / eigenvalue spectrum
• added a new utility function get_point_diagnostics in utility.py that extracts the correct diagnostics file from the Auto-07p output for a given solution
• changed get_solution_stability and get_solution_eigenvalues to use the new function in utility.py