Fix #494

If a row is full, don't bother allocating a new one, just return it.

Use the last populated row as a hint for the size of new rows.

Simplify checkSheet to remove row map

* Added accessors for Getting/Setting Page Margins

* Added test cases

The inline string struct is actually the same
as the shared strings struct, reuse it.

Note that Go version 1.10 is required.

Fixes #462

- Testing case for set and get doc properties
- Update charts struct XML tags

This adds outlinePr support, with the summaryBelow attribute
which defaults to true.

Closes #304

Signed-off-by: Michael Harris

new feature: protect sheet support, relate issue #273

Change `allowBlank`, `ShowErrorMessage` and `ShowInputMessage` type as boolean, add new field `ShowDropDown`, change fields orders follow as ECMA-376-1:2016 18.3.1.32.