copy_from/copy_to documentation (cursor.rst) incorrect

The documentation for the copy_from/copy_to cursor methods is incorrect and misleading. These methods expect a buffer size as the 5th argument (not counting self) and a sequence of column names only as the 6th argument.

I just wasted 3 hours trying to find out why the following wouldn't work:

cursor.copy_from(
    self.io,
    self.table_name,
    self.COLUMN_SEPARATOR,
    self.NULL_LITERAL,
    self.column_names
)

It kept failing with this error:

...
  File "pg_copy.py", line 51, in copy_from
    self.column_names
TypeError: an integer is required

Only when I went to the psycopg2 source code and started learning about PyArg_ParseTupleAndKeywords and other nasty Python internals it began to dawn on me that I was not insane and a "size" argument needed to be passed before the "columns" argument.

I'm now passing the latter as a keyword argument ...

cursor.copy_from(
    self.io,
    self.table_name,
    self.COLUMN_SEPARATOR,
    self.NULL_LITERAL,
    columns = self.column_names
)

... but the documentation should be fixed to save others from this ordeal.