This closes #1012, support specify the formula in the data validation range, and update the documentation for the `AddPicture`

- Make unit test on Go 1.7
- API documentation updated

Co-authored-by: xuri <xuri.me@gmail.com>

Co-authored-by: NStani Michiels <git@rchtct.com>
Co-authored-by: xuri <xuri.me@gmail.com>

New API: `SetRowStyle` support for set style for the rows
Update documentation for the `GetRows`, `SetCellStyle` and `SetColStyle`

- Make variable name more semantic
- Reduce cyclomatic complexities for the formula calculate function
- Support specified unzip size limit on open file options, avoid zip bombs vulnerability attack
- Typo fix for documentation and error message

Update documentation for `GetCellValue` and simplify code

Reduce cyclomatic complexities for the formula calculate function and update documentation for the API: `MergeCell` and `GetCellValue`

This closes #979, fix the data validation deletion issue and tidy the internal function in the source code

- support escaped string literal
- maximum character limit added
- fix missing preserve character in some case
Co-authored-by: xuri <xuri.me@gmail.com>

* Fix `SetDropList` to allow XML special characters

* This closes #971, allow quotation marks in SetDropList()

This patch included a XML entity mapping table instead of
xml.EscapeText() to be fully compatible with Microsoft Excel.

* This closes #972, allow more than 255 bytes of validation formulas

This patch changed the string length calculation unit of data
validation formulas from UTF-8 bytes to UTF-16 code units.

* Add unit tests for SetDropList()

* Fix: allow MaxFloat64 to be used in validation range

17 decimal significant digits should be more than enough to represent
every IEEE-754 double-precision float number without losing precision,
and numbers in this form will never reach the Excel limitation of 255
UTF-16 code units.

- Escape XML character in the drop list
- Fix incorrect character count limit in the drop list
- Fix Excel time parse issue in some case
- Fix custom number format month parse issue in some case
- Fix corrupted file generated caused by concurrency adding pictures

This closes #873, make the sheet names are not case sensitive for `NewSheet`, `GetSheetIndex`, `DeleteSheet`

- Rename exported field `File.XLSX` to `File.Pkg`
- Exported error message

This closes #861, support concurrency get cell picture and remove unused internal function `getSheetNameByID`

- Fix incorrect scope when getting defined name
- Update docs: use column number instead of index on get column width