add 6to5-node --extensions test
add hasType traverse test
add util list test
add destructuring no element test
add jsx elements to traversal visitor keys
allow let scope access within FunctionDeclaration, add _block-hoist helper transformer - fixes #77
add util.ensureExpressionType which will change a node from a declaration to an expression
forbid function declarations that reference block scoped variables
add support for exit traversal functions to replace the node
add jsx and react transformer