Add an option to limit glob task concurrency

There are hard limits in some OSs to the amount of files that can be open at
one time. To prevent EMFILE errors, this option can be used to restrict the
number of files open at once.
Add documentation of limit option in glob
Add dest task

This is more or less a compliment task to glob. When you are reading
multiple files, sometime you want those files to go to one place and that is
what this task is accomplishing.
Add tests for dest
Add dest to lib/index file
Add dest to README with usage information
Merge pull request #8 from sourrust/concurrent-limit

Glob concurrency limits
minor tweak
minor tweak and updated build
Merge branch 'sourrust-task/dest'
bumped version