Remove duplicate classes topic from C# guide

[pkulikov]

Combined C# Concepts classes article into the Classes (C# Programming guide) article.

Additionally:

• Inlined small code pieces as it makes a source Markdown file more readable.
• Minor editions.

Fixes #964

In tandem with PR dotnet/samples#8

[pkulikov]

@BillWagner I put WIP as I also want to move the example snippet to the samples repo.

[mairaw]

@pkulikov so we have a current work item (#1255) that we haven't been able to finish yet (it was supposed to be automated) but I manually change some PRs when I see they're touching snippets in these codesnippet folders.

The first time we migrated these topics, they erroneously broken down each sample into these tiny little snippets. But we do have the snippets in the samples repo already and you can see how the topic should have looked like if it got migrated correctly the first time here:
https://raw.githubusercontent.com/dotnet/docs/migration_csharpvb_reexport/docs/csharp/programming-guide/classes-and-structs/classes.md

So the original snippet for this probably lives here:
https://github.com/dotnet/samples/blob/master/snippets/csharp/VS_Snippets_VBCSharp/csProgGuideObjects/CS/Objects.cs

But you can probably change the samples location to ~/samples now that they don't live in this repo anymore. Something to test.

[pkulikov]

@mairaw interesting that that file with a lot of snippets doesn't contain snippets for the topic in interest; as if those were cut out of the file.

I've made the PR in the samples repo to move the snippet to programming guide snippets here:
https://github.com/dotnet/samples/tree/master/snippets/csharp/programming-guide/classes-and-structs

I assume the old way to link snippets from the Markdown files continues to work even when snippets are in the different repo.

This PR is ready for review.

[pkulikov]

@mairaw I've just realized that, of course, build fails - I should wait for PR dotnet/samples#8 in the samples repo to be merged in the repo. However, that would break current master here. How do I go from here? (Option: update PR in the samples repo not to break master here.)

[mairaw]

It's something we also need to understand better ourselves. It's been in my to-do list to talk to the engineering team about this workflow. When I catch a break, I'll take a look at your changes here and there. Exciting times! 😄

[pkulikov]

We need a notion of tandem PRs :)

[pkulikov]

@BillWagner there was the merge conflict with master; I've resolved it with the latest commit

[pkulikov]

@BillWagner and we should merge this PR as fast as possible: all other PRs do not build because of this one.

[BillWagner]

@pkulikov Overall, this is a great improvement to combine these two topics. There were a couple sentences that could be misinterpreted. I offered suggestions for other wording. Once that's done, I'll

Thanks again.

[BillWagner]

There are a few sentences here that could be more clear:

If the class is not declared as static, client code can create instances of a class or objects which are assigned to a variable.

Consider: "If the class is not declared as static, client code can create instances of it. These instances are objects which are assigned to a variable."

If the class is declared as static, then only one copy exists in memory and client code can only access it through the class itself, not an instance variable.

Consider: "If the class is declared as static, you cannot create instances, and client code can only access it through the class itself."

[pkulikov]

@BillWagner thank you for feedback, I've updated wording as you've suggested.

[mairaw]

If you approved this @BillWagner, I'll merge it then because all builds are breaking now because the samples change is in but not this one.