minmax: Only read newer files and write minmax.old

When updating the minima and maxima of several files in minmax,
write old values to minmax.old and do not read older files again.
split: Strip variable SPLIT_DROPSUFFIX
common: Strip variable DROPSUFFIX
scripts: Number of processed lines in awk scripts
split: Print number of processed lines
downsampling: Targets showdata and info fixed

Show filenames of down sampled data and always set description so
it can be used when including downsampling.mk in other makefiles.
downsampling: Read each file only once
downsampling: Print number of processed lines
downsampling: Do not reread file for future column
link_downsampling: Basic structure
link_downsampling: Links to down sampled data

Code from main dir makefile is moved to link_downsampling.mk to create
links to data in downsampling subdirectory and call the makefile there
by defining the variables TIME_UNIT, SAMPORIG and REDUCTION_FACTORS.
showmacros: Nicer spacing
histogram: Basic structure
histogram: Calculation of 2D histograms
histogram: Plotting of 2D histograms

The free energy landscape is plotted.
histogram: Calculation of 1D histograms
histogram: Calculation of 1D free energy landscape
histogram: Plotting of 1D histograms

The free energy landscape is plotted.
histogram: Calculate for lowest sampling time only
histogram: Reference file search improved (1)

Omit suffixes piece by piece to exactly match filenames.