Function `GetCellValue()` performance improvement by avoid repeating deserialization, relate issue #70.

- Unify the index row number index of functions `SetRowHeight()` and `GetRowHeight()` relate issue #68;
- Unify the return value data type of functions  `SetColWidth()` and `GetColWidth()`;
- go test updated

- Make function `TitleToNumber()` exportable, note that function `ToAlphaString()` return value calculation changes, get more info from go doc. Relate issue #63;
- Readme and go doc updated

- Function `formattedValue()` performance improvement by avoid repeating deserialization, relate issue #64;
- Make function `ToAlphaString()` exportable, relate issue #63

- Handle pre-defined number format set of cell when set cell value with `time.Time` data type, related issue #62;
- go doc updated

- Support insert new lines into shape, relate issue #38, note that the format set parameter of function `AddShape()` changed;
- go test and go doc updated

- go test updated;
- Fix typo

- go test updated

- Simplified code

- Add a donation link, related issue #57  ^_^

Priority cell style, when the cell and the column at the same time with the style attribute. Relate issue #54 and #56.

- gofmted with -s

- go doc and go test updated

- Function `SetCellValue()` support `time.Time` data type parameter, relate issue #49;
- go doc and go test updated

- Drawing `nvPicPr` element ID property calculation changed;
- go test updated

- go test updated

- go test updated

- Function `GetRows()` doc updated, relate issue #43;
- go test and embed template updated

- Readme updated;
- go test update

- Doc for function `GetRows()` updated, relate issue #43;
- Fix doc typo in `xmlContentTypes.go`;
- Default template updated;
- Readme updated;
- go test updated

- go test updated

- Typo fixed;
- go test updated

Fix return index error in function `GetSheetMap()`;
Fix return worksheet name error in function `GetSheetName()`;
go test updated

- Optimize deserialization operations;
- README updated, add go version required notice

Performance enhancements, remove redundant XML element checking logic. Relate issue #29. The benchmark report of the current version of this library is shown on the wiki page.

- go test updated

- Set text in cell align support, note that the parameters of the `SetCellStyle` function have changed;
- go test updated