v4.2

Release 4.2 of the vcf2prs script - first one to be publicly accessible.

v4.2.13
-It supports calculations on multiple samples.
-It supports calculations on mixed-ancestry individuals.

v4.2.17
-Added PRS reference file for STRATEGIC study
-Added numpy as a required package in requirements.txt
-Cleanup of the readme file

v4.2.19
-Modified requirements (pyVCF3 instead of pyVCF, as suggested by users)
-Improved input reading (allowing its use with PRS files with extra commented lines at the beginning)
-Renamed dataframe column in the R standalone script, to match the current name of the column in the input files