2019-10-31  0.1:  first alpha version


2019-11-19  0.2:  first beta version
                  
                  Previously, when the times of symbolic links of class 1 or class 5 tiers had to be inferred,
                  the program would cycle through all available class 4 tiers and pick the minimum and the
                  maximum as the link boundaries. Starting from this version, it will instead cycle through
                  a selection of class 4 tiers (in order of preference) and infer the links using one tier only.
                  If none of the tiers in this selection are available, an error is thrown.
                  
                  The command line parameter --list-reference-tiers has also been added which allows the user
                  to retrieve this 'tier hierarchy'
                  
                  Fixed bug which caused the order of tiers not to be preserved.
                  
                  If the time of a singular symbolic link cannot be inferred, the program now aborts instead of
                  simply issuing a warning.
                  
                  Removed prospect of support for specifying mutliple referenced files (the -r option now
                  demands exactly one file name and does not allow for a comma-separated list of files names).
                  
                  The program now throws an error if either the input our output file cannot be found.
                  
                  Greatly improved in-code documentation.
