Changes:
- Merging from Alistair Dunn fork into main code base general fixes, R-code fixes, documentation fixes
- Fixing Hamiltonian Monte Carlo
- Simplifying processes across Length and Age models to reduce duplicate code
- Minor fixes across processes and observations in line with new parameter handling and validation
- Adding more unit tests to increase coverage
- Memory allocation limits in ADOL-C and BetaDiff (ADOL-C base)