added support of let statements and base support of block scoping for identifiers, cf #883
Added real block scoping support for let statements, cf #883
minor cosmetic changes
refactored block scope handling, cf #883
added block of statements support without prefix token, cf #883
added tests for let statement support
fixed issue #894: error thrown when `foo(var(x=1) x);` is met.
Merge branch 'let_stmt' of github.com:guyzmo/jshint into let_stmt
added error for double definition of a let variable, cf #883
added support for let expressions, cf #883
updated support for double definition, cf #883
fixed block scoping to avoid showing undefined warnings for consts (that already have an error). And added guards. cf #883
fixed destructuring assign in global context. Updated tests. cf #883