Add NET Core and NET 5 support.

[VPKSoft]

• Add NET 5 support.
• Add NET Core support.
• Update .NET Framework to 4.7.
• Update project format to Microsoft.NET.Sdk.
• Updated NuGet dependencies of the test and the demo project.

Side-effects:

• One test broken: InterleavedBitmapPaletteSerializerTests.cs, SerializeTest()

Other:

• Removed release binaries as they shouldn't be a part of a version control data.

[cyotek]

Hello,

Thanks for this PR. I've decided not to accept it for various reason - every file seems to have changed for example (whitespace issues?) and some of the corrections aren't the way I would have done them (for example the compile error due to the static type). The main reason though was I've been migrating many of our internal projects to multi-targeted SDK libraries and this is the first one I've got to that used Windows Forms. As a result, I wanted to do this myself by hand in order to determine any issues that I will encounter when converting the large number of other projects I need to process (for example dotbuild with resx files doesn't work and I need to find a better solution that deleting the resx files ;) ).

There is a branch in this repro called dotnet50 which includes a smaller set of changes to convert to multi-target SDK (targets 3.5, 4.0, 4.5.2, 4.6.2, 4.7.2, 4.8 and 5.0 (which I will hopefully merge in this week after doing some more testing, and potentially adding in .NET Core 3.1 which I forgot about).

Thank you again for the PR, I'm sorry I wasn't able to accept it this time.

Regards; Richard Moss