LD paper accepted in Genetics

Breaking:

• switch to C++17 and above standard
• option -v/--verbose takes integer value for different verbosity level
• remove temporary files in default. only keep them when the verbose level is >=3.

Improvement:

• CLI. run PCAone --groff > pcaone.1 to generate the manual that can be read by man ./pcaone.1
• refactor the halko code
• speedup projection and prediction with multithreading