Setting up CI and Nuget packaging for SpriterDotNet

[jonathanpmast]

Heya @loodakrawa, we forked this repository to set up a CI server and nuget package via appveyor. I figured we would at least PR it back upstream to see if if it is something you wanted to pursue. And possibly publish a nuget package onto nuget.org. I'm happy to make any changes if you're unhappy with the edits or want some additional help publishing to the primary nuget repo.

By and large functionally there's no changes; I just added a couple files to support appveyor and nuget packaging (appveyor.yml and SpriterDotNet.nuspec) and updated the Test project to try to make sure everything was still working :)

In order to have the monogame based project build in appveyor's environment I pulled out the monogame project template (basically just an msbuild target) and switched the dependency over to the monogame nuget package.

[loodakrawa]

Hey, thanks for the PR. Setting CI and nuget packaging is really a good idea. I will eventually publish this to the main nuget repo - but I first want to properly do the monogame plugin (work in progress).

Regarding this pull - it has merge conflicts. Could you please fix those and reopen it again? Also, the diff shows some changes that shouldn't be there - like CHANGELOG.md etc. Could you also make sure that only the real diffs show as changes? Thanks.

[jonathanpmast]

No worries. I think maybe I squished too many commits into one possibly when i merged develop into my feature branch in my fork. I didn't look at your contribution guidelines until late in my dev work :)

I'm interested in the monogame branch as well so I might wait until you finish that up and just clean this up and re-submit after those changes.

[loodakrawa]

I updated the MonoGame plugin and published it to NuGet: https://www.nuget.org/packages/SpriterDotNet.MonoGame/

I'll close this PR but feel free to open another one if you have any contributions. Cheers