Save metadata in tif files

[gabriel-ing]

At the moment only saving pixelsize and unit but it should be super simple to do (I actually have done this in 2 lines of code but not tested yet)

[gabriel-ing]

Took a lot more than 2 lines of code to fix this, I had an issue with unicode text not being saved in Tif files, so to fix this I changed any µ to u, but then just removed any unicode characters not present in ascii from the metadata. This still does not always work so requires further investigation.

[jrobsontull]

@gabriel-ing Looks like tifffile encodes the metadata to ascii before saving (see tifffile.py). If you are seeing unicode text in your metadata after reading the data in, sounds like you need to decode it first. In the first instance as a safety net before saving, you could decode and then encode to ascii, prior to tifffile.imsave().

for key in metadata.keys():
    value = metadata[key]
    metadata[key] = value.decode('some_encoding').encode('ascii', 'replace')