MTFontManager manager is nil

[petersktang]

manager is accessible to external apps, fontManager is inaccessible, the below fixes manager nil issue.

public class MTFontManager {

static public private(set) var manager: MTFontManager = {
    MTFontManager()
}()

let kDefaultFontSize = CGFloat(20)

static var fontManager : MTFontManager {
    return manager
}

[petersktang]

Included the above in pull request

[mgriebling]

Pull merged.