modifying reader attributes does not modify underlying tiff-class attributes

[bryantChhun]

after building a reader:

mmr = MicromanagerReader(<folder to tiff files>)

modifying an attribute such as frames will not change the underlying tiff-class's attribute

mmr.frames = 10
print(mmr.reader.frames)
>>> not 10

This is a problem in cases where a acquisition quits before it's scheduled to finish -- so the metadata reflects a different dimensionality than actually exists. Simple case is when you specify a 100 frame time series at the start but end the collection after 50 frames.

Solution:
change reader attributes to getters/setters that modify and return the underlying tiff-type attribute

[bryantChhun]

fixed in pr #17