Update rule for long function declarations to specify effects (`async…

…`, `throws`) should be written on the line after the closing paren (airbnb#205)

Add rule to prefer opaque generic parameter syntax (airbnb#193)

Infer Swift version from Package.swift swift-tools-version (airbnb#180)

Add info about Swift Package Manager command plugin to README.md (air…

…bnb#176)