v6.1: release MagIC 6.1

• Now support input resolution in spectral space directly specifying l_max and m_max. This now also allows resolutions with m_max /= l_max (useful some mechanical forcings)
• Implement support for a linearized version of MagIC to speed-up the estimate of critical Rayleigh numbers. Use it with mode=5 and a range of azimuthal wavenumbers from m_min and m_max. Files drift_[a]sym.TAG and growth_[a]sym.TAG then contain the time series of drifting frequencies and growth rates for the corresponding wavenumbers for both equatorally-symmetric and antisymmetric modes.
• Support for phase field based on Hester et al., 2020. Right now time schemes with an assembly stage are not supported.
• Deep debug of non-initialized arrays