Plot SFR history from Gadget's sfr.txt file.
-h: help
-m: plot with Madau & Dickinson (2014) (require b option)
-o: plot with observational data (require bz option)
-b: boxsize (Unit: Mpc/h)
-l: plot SFR in log scale
-z: set x axis redshift
-Z: set x axis redshift and set max of xrange
-s: save figure (png only)
eg) sfrplot -mob 10 -lZ 15 -s sfr.png data1/sfr.txt data2/sfr.txt