Improve treatment of multiple bullets at once and calc_end_start_time()

First, we don’t need separate regexes in script since we check for
scope, so single regex per item is [supposed to be] fine for all bullets
types. Close #139
Second, since we have bullets with different length (1 or 3 chars), we
need to make sure that eol would be correct for calc_end_start_time(),
and since done tag may have or miss whitespace before date, need to make
sure that date would be parsed correctly