devshm element

This is a an element intended as an alternative to the lvsshm element.

It waits for GWF files to be added to a directory and feeds them to the pipeline.

While the intention is to read files from /dev/shm/kafka/foo, it really has nothing to do with shared memory, it just reads files out of a directory. However, it does make assumptions about data in the files. In particular, it assumes that the files contain 1 second of data which is true, currently, for the files written to /dev/shm/kafka/*.