Version 2.2.0

Introduce AliSim, an ultrafast and realistic sequence alignment simulator for phylogenetics, as an extension of IQ-Tree.
User Manual of AliSim is available at http://www.iqtree.org/doc/AliSim

- Update 1st June 2022:
Bugs fixed:

• Output long sequence names.
• Only show AliSim commands if users specify --alisim commands

- Update 25 March 2022:

• Improve indels implementation.
• Bug fixed: GC+I (continuous Gamma rate variation + invariant proportion sites)