hn2016_falwa v0.1.5c

Updates from v0.1.4:

• Included a function 'static_stability' to compute static stability from potential temperature field.
• Fixed a bug in outputing equivalent latitude in the function 'qgpv_Eqlat_LWA'. Other related subroutines are not affected.
• A beta version of function 'Solve_URef_noslip_hemisphere' is updated. It can only be used to compute eddy-free reference state in no-slip boundary conditions.