Extract loader to separate lib

[B-Reif]

This library seems to implement two separate pieces of functionality:

• the monogame pipeline implementation, and
• an Aseprite loader implementation.

As a separate package, the loader implementation could serve any kind of dotnet user, whether they're using the pipeline tool or not. The pipeline lib could then use this as a dependency and contain only the pipeline-related logic.

[AristurtleDev]

@B-Reif I'm sorry it took so long to get back on this (life happens), but if you're still looking for something like this, I have released AsepriteDotNet as a separate library that is framework/engine agnostic and uses native dotnet types.

I also have an update for this library coming soon that also provides this for monogame specific scenario for users that don't use the content pipeline too.

[B-Reif]

I don't anymore, but thank you!