Specified folder exclusion

[ddukstas]

Hello!

I needed to get a checksum of a directory, excluding some folders in it when calculating that checksum. So I added a new param 'exclude' to specify folders which will be excluded from calculation of checksum of root directory. 'exclude' is an array and its elements are names of folders which are needed to be excluded.

I guess it might be an useful feature for others as it was in my case.