Try netstandard where possible

Replace net452 with net40 build

Use OpenXML 2.7.2 for all targets

Add a basic test for OpenXml - which currently breaks in .NET Standard 2.0

Merge remote-tracking branch 'origin/drop-dataTable-asEnumerable' into netstandard2 ...

# Conflicts:
#	ClosedXML/Excel/Cells/XLCell.cs

Improve color support and more

Add ability to insert data of datatable directly without converting to Enumerable - preparation for .NET Standard

Allow rename of sheet by changing case

Add APPVEYOR environment variable support

Change to VS 2017 Preview image to support .NET Standard 2

Merge branch 'develop' of https://github.com/ClosedXML/ClosedXML into netstandard2 ...

# Conflicts:
#	ClosedXML/ClosedXML.csproj
#	ClosedXML/Excel/Drawings/XLPicture.cs
#	ClosedXML/Excel/IXLTheme.cs
#	ClosedXML/Excel/XLWorkbook.cs
#	ClosedXML/Excel/XLWorkbook_Load.cs
#	ClosedXML/Excel/XLWorkbook_Save.cs
#	ClosedXML/Properties/AssemblyInfo.cs
#	ClosedXML/Utils/GraphicsUtils.cs
#	ClosedXML/XLHelper.cs
#	ClosedXML/packages.config
#	ClosedXML_Examples/ClosedXML_Examples.csproj
#	ClosedXML_Examples/Properties/AssemblyInfo.cs
#	ClosedXML_Examples/packages.config
#	ClosedXML_Sandbox/ClosedXML_Sandbox.csproj
#	ClosedXML_Sandbox/Properties/AssemblyInfo.cs
#	ClosedXML_Sandbox/packages.config
#	ClosedXML_Tests/ClosedXML_Tests.csproj
#	ClosedXML_Tests/Properties/AssemblyInfo.cs
#	ClosedXML_Tests/packages.config

Implement .NET standard as far as possible. ...

System.Drawing.Bitmap is still missing - hence the XLPicture API is incomplete

Revert change that introduce bug in parsing shared fomulas

Allow duplicate picture names when loading a file, but don't allow duplicate Ids

Optimise calculation chain generation and introduce new SaveOptions

Add helper function: IXLCell.HasArrayFormula and improve loading of array formulas

Update test cases for array formulas

Merge pull request #442 from igitur/remove-IsNullOrWhiteSpace-net35-workaround ...

Remove obsolete XLHelper.IsNullOrWhiteSpace

Remove obsolete XLHelper.IsNullOrWhiteSpace

Allow ridiculous, but valid formulas, e.g. =+++++++MID(A3,3,5)

Allow minimum of 3 parameters for VLOOKUP / HLOOKUP

Default range lookup to true if parameter is EmptyValueExpression

Clear list of deleted worksheets after save to prevent exception on multiple saves.

Check for null and fallback to workbook if worksheet range not found.

Load named ranges in worksheet scope as is, without validation.

Add unit test

Allow clearing of cell contents by setting null value.

Merge pull request #256 from ClosedXML/develop ...

Latest develop to master

Merge branch 'develop' of https://github.com/ClosedXML/ClosedXML into issue347-floor-function-parameters

When copying a worksheet, named ranges on the source worksheet have to point to the new destination sheet. Fixes #416