use const and let instead of var

[Brooooooklyn]

Use const and let instead of var
And use semicolon in interface

[Brooooooklyn]

@mhevery I'm wondering if use let and const is a better way to write typescript, and I remove the var in lib files.

And also , I fix some style in codes such as == and ',' in interface and type

[mhevery]

Yes let and const are better. Old habits die hard.