RomainFeron/PSASS: Version 2.0.0

This version includes a partial rewrite of PSASS with some CLI changes, hence the up in major version number. Major changes :

• PSASS CLI now has subcommands. The old PSASS is now accessible with the subcommand "analyze"
• FST in a sliding window does not show the number of bases with FST > threshold anymore, but rather the FST between populations for the given window.
• PSASS now output metrics at the beginning and at the end of contigs (for values lower than 1/2 window size). Calculations are performed on whatever bases are covered by the window.