Documentation bug in ImageReader

[omsai]

The docstring for ImageReader() mentions a non-existant GetImageReader():

https://github.com/CellProfiler/python-bioformats/blob/0d47e384d5ab8669cfcbf43b8900b0d544aa274b/bioformats/formatreader.py#L550

...but it should probably instead mention get_image_reader(). I would submit a PR, but it looks like additional statement(s) are needed, perhaps to initialize javabridge, because if I use any random key for get_image_reader() it fails, and dropping into the debugger indicates it's because javabridge.jutil.get_env() returns None

One can also run tests on docstring example code using doctest from the standard library or similar.