Swift 2 support

[taku0]

I have updated my old implementation #74 to support Swift 2.1 syntax #96 #125.

• Fixed indentation
• Fixed highlighting
• Supports playground comment syntax https://github.com/chrisbarrett/swift-mode/issues/96#issuecomment-137503789
• Supports fill-paragraph on comment
• Added extensions to Imenu
• Added some tests that current implementation fails (not only Swift 2.1 syntax but including Swift 1.0 syntax)

This patch also fixes #85 #59 #72 #35, like #117.

Tested with Emacs 24.5.2. All tests are passed with some cheating. I modified some tests a bit.

I don't expect you to merge this large complex patch. Please copy some parts not related to indentation if you like. I'm sorry for that you cannot cherry-pick simply because I have fixed both highlighting and indentation (or even worse, multiple issues) in same commit. I should have splited commits into those related to indentation and others, and made separate PRs.

[ap4y]

Hey @taku0, thanks for the PR. I been doing the same slowly in my local branch too, will try to cherry-pick from your branch.