Test on SLTimer output

[drphilmarshall]

Once SLTimer can produce "sample" time delays (and it's close, I think), we can test to make sure we get an H0 out from one or more of its output files. This test should be carried out through a new notebook.

• Start SLTimer test notebook
• Upgrade read_in_from() method to get Fermat potential differences from header Test on SLTimer output #29