Enable single-writer multiple-reader access to trace files.

[maij]

Fixes #224.

By using the latest version of hdf5 we gain access to some extra features, including single-writer multiple-reader (SWMR) mode. We may wish to specify the exact version we want to use, going forward, to ensure backwards compatibility is more easily assured.

• [x] Test that I can read from a live trace file as it changes.
• [x] Verify the integrity of the traces (compare locally acquired version to version recovered from file)
• [x] I also checked that loading h5py files from previous library versions works well.
• [x] Speed performance, actually seems to have improved
  • Before
    • Storing 600,000 points takes ~ 260 +- 58 ms.
    • Storing 1500 points takes ~5.7 +- 4.7 ms
  • After
    • Storing 600,000 points takes ~ 230 +- 50 ms.
    • Storing 1500 points takes ~1 +- 4 ms

[maij]

Great addition! Do we need a minimal h5py version?

Nope! The current minimum in setup.py is 2.6.0 which supports SWMR.