Implemented GetCellError. Closes ExcelDataReader#466

Bumped version to 3.7.0 and updated README.md

Merge pull request ExcelDataReader#407 from ExcelDataReader/develop

3.6.0

Merge pull request ExcelDataReader#397 from ExcelDataReader/develop

3.5.0

Merge pull request ExcelDataReader#359 from ExcelDataReader/develop

3.4.2

Merge pull request ExcelDataReader#349 from ExcelDataReader/develop

3.4.1

Merge pull request ExcelDataReader#313 from ExcelDataReader/develop

3.4.0

Merge pull request ExcelDataReader#294 from ExcelDataReader/develop

3.3.0

Merge pull request ExcelDataReader#276 from ExcelDataReader/develop

3.2.0

Merge pull request ExcelDataReader#256 from ExcelDataReader/develop

3.1.0