Implement MetadataExtractor to get image dimensions and format

Merge branch 'netstandard2' into net40 ...

# Conflicts:
#	ClosedXML_Examples/ClosedXML_Examples.csproj
#	ClosedXML_Sandbox/ClosedXML_Sandbox.csproj

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

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

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

Optimise calculation chain generation and introduce new SaveOptions

Update test cases for array formulas

Implement more Information functions - specifically around errors

Parse formulas correctly if they already contain an error.

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

Initial implementation of CalcEngineExceptions

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.

Add unit test

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

Fall back to display name if table name is missing.

Allow new style functions with period, e.g. FLOOR.MATH ...

Better parsing exceptions
Implement FLOOR.MATH

Reformat indentation.

Allow table field rename by setting cell value. Fixes #285

Correctly implement MOD function