This is the updated patch of "Add :caption attribute to #+ATTR_LATEX property"

If possible, please include it to master

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This feature is very useful when you export org to latex with custom
caption command, for example:

#+ATTR_LATEX: :caption \BiTableCaption{caption 1}{caption 2}
|---+---|
| x | y |
|---+---|
| 1 | 2 |
|---+---|

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