Added option -D (--sortcriteria) to allow more options in deciding which file to keep.
Just three sub-options for now (mtime, alphabetical or order in which paths were entered).
Currently no checking for invalid options (anything other than aAmMpP will be ignored).
fixed missing "break" in switch for sort criteria to select original
removed redundant line
Tidied up "-o --output" option and documentation.
Note -o now has non-optional second argument;
	nil output is specified as -o ""
Fixed error in calculation of total duplicates.
Merge branch 'devel' of https://github.com/SeeSpotRun/rmlint into develop