Support single expression members

[sgade]

What's in this pull request?

Adds support for single-expression members (on classes and structs). This is part 2, following #75.

Example:

class SingleExpressionMembers {
    var one: Int {
        10
    }

    var two: Int {
        get {
            20
        }
    }
}

internal open class SingleExpressionMembers {
    open val one: Int
        get() = 10
    open val two: Int
        get() = 20
}

Does this resolve an open issue?

Yeah, it resolves #72.

Checklist for submitting a pull request:

• [x] Your code builds without any errors or warnings (warnings when running prepareForBootstrapTests.sh are OK).
• [x] You ran the unit tests and Bootstrapping tests for your platform.
  • [x] If you changed any .kt files in the Test cases folder, you also ran the Acceptance tests.
• [x] You have added new tests that check your changes (if possible).
• [x] This pull request is targeting the development branch (if you're contributing code) or the gh-pages branch (if you're contributing to the website).

[vinivendra]

Ok, the release is ready, just waiting for this. Let me know if you'll have time to add the test now, otherwise I'll merge the PR and we can add it later.

[vinivendra]

Alright, I'm merging it (sorry, I'm kind of in a hurry here). Great job and thanks again :)