WaveorderReader should give more informative error messages

[talonchandler]

The current WaveorderReader error messages can be slightly confusing. For example:

python
>>> from waveorder.io import WaveorderReader
>>> WaveorderReader('./2T_3P_16Z_128Y_256X_Kazansky_BF_1')
<waveorder.io.reader.WaveorderReader object at 0x7f7d1807cc70>
>>> WaveorderReader('./2T_3P_16Z_128Y_256X_Kazansky_BF_1/2T_3P_16Z_128Y_256X_Kazansky_BF_1_MMStack_Pos0.ome.tif')
ValueError: Specific input contains no ome.tif files, please specify a valid input directory
>>> WaveorderReader('./nonexistent'))
FileNotFoundError: No compatible data found under ./nonexistent, please specify the top level micromanager directory.

I might suggest that:

• trying to open a single multipage .ome.tif file should give a different error message like "WaveorderReader expects a directory of .ome.tif files, not a single file.". As written the error might make it seem like the ome.tif is invalid/corrupt.
• trying to open a nonexistent file/folder displays the message "This file/folder does not exist on the file system, please check your path and provide a directory." As written the error makes it seem like the reader only reads micromanager directories. Also, the error makes it makes it seem like the files are invalid/corrupt, when in reality it's a path issue.

[talonchandler]

FWIW these messages have caused me and at least one user some difficulty in using the reader. I think it's worth the effort to carefully choose error messages.

[talonchandler]

Closing this...I/O has moved to iohub which now has much clearer error messages.