Rev 0.22

+! Revision 0.22
! Date: Mar 9th, 2018
! - a new procedure called use_extra_configuration is used to set general gnuplot settings
! - new type for labels (xlabel, ylabel, zlabel, title,...)
! - all lables now accept text color, font name, font size, rorate by degree
! - Secondary axes can use different scale (linear or logarithmic)
! - subroutine plot2d_matrix_vs_matrix(xmat,ymat)
!    now plots a matrix columns ymat aganist another matrix column xmat
! - added more examples