- update to 3.1.2:
* #1963 Cannot read worksheets in read-only mode with locally
scoped definitions
* #1974 Empty custom properties cause invalid files
* #1881 DocumentProperties times set by module import only
* #1947 Worksheet-specific definitions are missing
* #1156 Table filters are always overriden
* #1360 Can't read some ScatterCharts if n
* #1724 Problem with multilevel indices in dataframes
* #1772 Problem with category indices in dataframes
* #1786 NamedStyles share attributes - mutables gotcha
* #1851 Allow print area to be set to None
* #1852 Worksheet for print title and print areas can't be found
* #1853 Custom document properties that are strings can be empty
* #1858 ConditionalFormatting lost when pivot table updated
* #1864 Better handling of defined names
* #1904 dataframe_to_rows() misalignment on multiindex
* #1912 Excel doesn't like xmlns:space on nodes with only
whitespace, which it treats as empty.
* #1942 Exception when print areas use table references.

* Adding tables in write-only mode raises an exception.