Phconvert

What's new?

This version adds type checks when saving Photon-HDF5 files as described in this [Pull Request](https://github.com/Photon-HDF5/phconvert/pull/3).

In this version a few fields have been renamed and a few were added:
- `acquisition_time` -> `acquisition_duration`
- `comment` -> `description`
- `funding` (new field)
- `license` (new field)

Additionally:
- The notebook to convert files have been updated to be easier to follow for users new to Jupyter.
- The default URL saved in the file is now http://photon-hdf5.org

What's new?
- Still one forgotten rename (e05873a08f1e22163cfaa2695fe2699d55e3df62)

What's new?
- Finish renaming some fields forgotten in the previous release (bd4032d1b0667e13fed3f885191298e4468eb8fe).

What's new

Some fields were renamed, namely:
- `laser_pulse_rate` -> `laser_repetition_rate`
- `alex_period_excitationN` -> `alex_excitation_periodN`

Also, always save _binary ASCII strings_ (instead of _unicode strings_) to maximize file compatibility.

What's new?

When saving Photon-HDF5 files with `phconvert`, the fields in `detectors_specs` are now casted to be the same type as `detectors` array.

This change does not affect users reading Photon-HDF5 files in Python and MATLAB, but it may simplify the life (and potentially remove a source of confusion) for users using strongly typed languages.