The end of a date range should not be inclusive

[stupakov]

If I make an event that spans 1990-1993, and another that spans 1993-1994, I would expect those not to overlap.

However, the current implementation interprets these ranges as:

    Jan 1, 1990 - Dec 31, 1993 and
    Jan 1, 1993 - Dec 31, 1994. 

Thus they overlap by a year.

Wouldn't it be more appropriate to interpret it as:

    Jan 1, 1990 - Dec 31, 1992 and
    Jan 1, 1993 - Dec 31, 1993. 

[cheeaun]

This was discussed in #9 . My reasons were explained in that thread.