allow access of MetadataManager options as attributes

[d-w-moore]

Allowing this means we can probe the current value. E.g. obj.metadata.reload is True (as that's the default) but obj.metadata(reload=False).reload reflects the modified value of False

[d-w-moore]

Not relating to this, I'll also observe that the recent pull request which addressed #709 also (in providing reload as an option) addressed #768, though that is currently undocumented in the commit message.