add function to get information out of a mark store
add function to get information out of a mark store

__mark_get:
    + function to get marks and information about marks
    + arguments:
        + "-y= | -m= | -d=" date options
        + "-s=" store location
        + "-r=" range of days
    + behaviour:
        + if no specific date argument is given the current date is used.
        + if day is set to 0 a small summary of the month is printed
        + if range is given all marks in the range are printed

fischerling/mark