Add support for netstandard 1.0

[eloekset]

With .NET Core 1.0 released, this project should provide a NuGet package that targets netstandard 1.0 to support as many platforms as possible. https://docs.microsoft.com/en-us/dotnet/articles/core/porting/libraries#targeting-the-net-standard-library

I forked this repo and merged PR #11 as a starting point, and by tweaking a bit and leaving out the methods that take DatePrecision as parameter, I was able to build a netstandard 1.0 assembly. However the xproj project type doesn't support the Shared Project model, so the project and file structures are messed up in my branch right now. I havent published the branch because of this.

I think it's possible to have a single xproj with a project.json that defines all platform targets and builds net35, net40, netcore45 and netstandard1.0 assemblies out of a single project, but I know Microsoft is planning on converting xproj back to csproj in a future release of the .NET Core tools, so I'm not sure whether converting to the single project approach is the right move now.

A safe approach would be to keep the -net35, -net40 and -netCore45 projects and move all files into a new xproj project and then add all files as linked files into the other projects.

[eloekset]

I've done an attempt to target .NET Standard 1.3, but ran into a reflection problem where GetMethod was used. It's not supported by .NET Standard 1.3, and I'm not sure if GetDeclaredMethod would works as a replacement. As a first step I've opened PR #14 targeting .NET Standard 1.6. Then we can build upon that to target lower API levels if needed.

[omarpiani]

Hehe, we see again @eloekset, I make a +1 to this request

[eloekset]

I've switched to Shouldly https://github.com/shouldly/shouldly for my .NET Standard projects. It supports .NET Standard 1.3.

[omarpiani]

me too, but is not kind to say here :)