split: Split trajectories in several parts

If SPLIT_FUTURE is 1, each data file is split after each line where
the last column is 0.  If SPLIT_FUTURE is 0, each file is split into
two parts.  If not set, SPLIT_FUTURE defaults to IF_FUTURE or to one.
split: Split pca data in main directory
downsampling: Basic structure
downsampling: Down sampling for all starting points

Split data is written to splitdata/ in main directory,
or, for the standalone version, in current directory.
If data shall not be split, SPLIT_FUTURE is set to 2.
downsampling: Compatibility with SPLIT_DROPSUFFIX
downsampling: Target and links for use in main dir
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: 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