Add extra argument "Linktype" to SetCellHyperLink

it support "External" and "Location"
Signed-off-by: NYoungwan Kim <y103.kim@gmail.com>

- go test updated

- godoc updated

- go test and godoc updated

- godoc updated

- Readme and go test updated

- Format code and update readme

- go test updated

- go test and godoc updated

SHEET.GO: Fix small typo

Adds a '{' to the example for sheet.GetSheetMap()
Signed-off-by: NMark Stenglein <mark@stengle.in>

- New function `NewStyle()` added and function `SetCellStyle()` has been exported, relate issue #72;
- go test and go doc updated

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