Feature Request: Support for reading and writing merged image data section

The README explicitly describes this feature as not supported / a non-goal:

Files written by the PhotoshopAPI do not contain a valid merged image in order to save size meaning they will not behave properly when opened in third party apps requiring these (such as Lightroom)

In my opinion, in order for the library to support more generic use cases, it could be nice to support the merged image data optionally.

It might conflict with the goal:

The PhotoshopAPI is built with performance as one of its foremost concerns. [...] As the feature set increases this will keep being one of the key requirements.

Hence I suggest:

• Default behavior does not change: merged image data is ignored when reading a file, no meaningful merged image data is written to a file.
• Reading and writing get some optional parameter to enable merged image data, e.g.:

  file = psapi.LayeredFile.read("file.psd", include_merged_image=True)
  file.write("file.psd", include_merged_image=True)

• We don't care about making the content of the merged image data consistent with the layers: That's the user's responsibility.

Let me know what you think - happy to discuss!