Update docstring, remove .5 factor and rounding
Update docstring, remove .5 factor and rounding

Major update of the top-level docstring to explain all the differences
compared to the MIREX 2015 matlab evaluation code. Remove the
multiplication by the .5 factor when computing the offset_tolerance,
since it turns out this not done in the MIREX evaluation. Also remove
the rounding down of onset/offset times.

faroit/mir_eval,faroit/mir_eval,craffel/mir_eval,rabitt/mir_eval,bmcfee/mir_eval,bmcfee/mir_eval,craffel/mir_eval,rabitt/mir_eval