add Compromises section to README
Merge pull request #4 from shapesecurity/compromises

add Compromises section to README
add link to shapesecurity/shift-parser-js
add shift-codegen-js link to implementations section
add link to shift-scope-js in README implementations section
README: add @Constellation's shift-traverse-js project to implementations
add optional SourceLocation to Node interface
Merge pull request #7 from shapesecurity/source-location

add optional SourceLocation to Node interface
fixes #5: move body attribute to IterationStatement interface
ES6 WIP