Support Swift language changes in Xcode 6.1

(Note these changes will not work with Xcode 6.0)

- Added UnicodeScalarLiteralConvertible protocol to JSON
- Added explicit unwrapping where needed e.g. optional NSURL (ideally
we should check for errors first before using the returned objects),
UITableViewCell constructor is now also optional
Set postDataKey in SwifterAccountsClient's post function
Add README note for Xcode 6.1 users
Fix getUserStreamDelimited(wrong url)
Replaced all `id: Int` with `id: String`, fixes #43.
Temporarily remove literal convertible protocol implementations, fixes #51
Fixing compile error

SwifterAuth.swift:69:55: error: value of optional type 'NSURL?' not unwrapped; did you mean to use '!' or '?'?
                NSWorkspace.sharedWorkspace().openURL(queryURL)
Add Literal convertible initializeris, fixes #51
Replaced all `id: Int` with `id: String`
Replaced all `id: Int` with `id: String` (found that at least 3 files)
Replaced all `id: Int` with `id: String` (User IDs and Direct Message IDs)

https://blog.twitter.com/2013/64-bit-twitter-user-idpocalypse
Fix postUsersReportSpamWithUserID
Fix iOS demo in 6.1
Redesigned logo
Fix logo width
Remove 6.1 branch note
Fix getStatusesUserTimelineWithUserID not returning specified user's timeline, fixes #57