Add rules from Erica Sadun

[jpsim]

Lots of good stuff in here that we could turn into SwiftLint rules: http://ericasadun.com/2015/11/17/a-handful-of-swift-style-rules-swiftlang/

Notably, the following rules should be straightforward to implement:

• The Rule of Conditional Binding Cascades (done in add ConditionalBindingCascadeRule #327)
• The Rule of Pattern Matching Keywords (done in Add pattern_matching_keywords rule #1800)
• The Rule of isEmpty (done in add rule to encourage checking isEmpty over comparing count to zero #206)
• Prefer Swift constructors to legacy ones (done in Prefer Swift constructors to legacy ones #242)
• Avoid terminal semicolons even though they compile (done in add trailing semicolon rule #203)

[marcelofabri]

@jpsim About "Prefer Swift constructors to legacy ones", do you see another way than keeping a list of known legacy constructors and checking for their presence?

[jpsim]

That was how I was thinking of doing it, yes!