handling gsla data (gzipped)

 * gunzipping files if they have a .gz suffix
 * acorn profile is actually a default profile
 * test for GSLA
 * updated README.md with GSLA example
Merge branch 'master' of github.com:aodn/go-go-duck
updated README.md
handling gzipped files on fs, probing fs automatically
some refactoring to worker, added tests
updated main README.md with origin of name
Merge pull request #7 from aodn/filesystem_probe

Filesystem probe