Add timeout?

[hyrious]

Can we add an option like diff_match_path.Diff_Timeout in sync mode? Since #396 may not be solved easily, this option can help reducing many issues about performance like #376

[quark-zju]

FWIW, diff_match_path.Diff_Timeout does not seem to actually work in its Javascript version. Whatever value it is set, the dmp diff algorithm takes the same time. And if the timeout is too small, the diff output is suboptimal (the computation for the more optimal diff is done but dropped due to the timeout logic). So in practice you always want to set it to a large value to avoid discarding the optimal diff output.