Handling extremely large number of TIFFs

[jakirkham]

In some cases, we are merging nearly 1000 individual TIFFs together. From the data standpoint, this is fine. However, from a metadata standpoint this is suboptimal. This is because we are storing the filenames in an HDF5 attribute. However, we start exceeding HDF5 size limitations for this attribute by doing this sort of thing. So we need to come up with another way to handle this metadata and/or an option to disable handling it.

[jakirkham]

Please see PR ( #437 ) for the fix.