What is nicely shortened? Consider this line from Orwell's 1984...
0---------1---------2---------3---------4---------5---------6---------7---->
When we are omnipotent we shall have no more need of science. There will be

If the limit is set to 70, a hard truncation would result in...
When we are omnipotent we shall have no more need of science. There wi...

Truncating to the nearest space might be better...
When we are omnipotent we shall have no more need of science. There...

The best truncation would be...
When we are omnipotent we shall have no more need of science...

Therefore, the returned string will be, in priority...

1. If the string is less than the limit, just return the whole string
2. If the string has a period, return the string from zero to the first
    period from the right
3. If the string has no period, return the string from zero to the first
    space
4. If there is no space or period in the range return a hard truncation

In all cases, the string returned will have ellipsis appended unless
otherwise specified.

Parameters:
    s = string to be truncated as a String
    min_pos = minimum character index to return as Integer (returned
              string will be at least this long - default 0)
    max_pos = maximum character index to return as Integer (returned
              string will be at most this long - default 75)
    ellipsis = returned string will have an ellipsis appended to it
               before it is returned if this is set as Boolean
               (default is True)
Returns:
    Truncated String
Throws:
    ValueError exception if min_pos > max_pos, indicating improper
    configuration
Usage:
short_string = trunc(some_long_string)
or
shorter_string = trunc(some_long_string,max_pos=15,ellipsis=False)