6.0.0

I'm extremely stupid and didn't commit as I go. To anyone reading this
I'm extremely sorry. A lot of these changes are very broad and I plan on
releasing Babel 6.0.0 today live on stage at Ember Camp London so I'm
afraid I couldn't wait. If you're ever in London I'll buy you a beer
(or assorted beverage!) to make up for it, also I'll kiss your feet and
give you a back massage, maybe.

packages/babylon/src/util/identifier.js

@@ -49,7 +49,7 @@ nonASCIIidentifierStartChars = nonASCIIidentifierChars = null;
 // offset starts at 0x10000, and each pair of numbers represents an
 // offset to the next range, and then a size of the range. They were
 // generated by tools/generate-identifier-regex.js
-var astralIdentifierStartCodes = [
+let astralIdentifierStartCodes = [
   0, 11, 2, 25, 2, 18, 2, 1, 2, 14, 3, 13, 35, 122, 70, 52, 268, 28, 4, 48, 48, 31, 17, 26, 6, 37, 11, 29, 3, 35, 5,
   7, 2, 4, 43, 157, 99, 39, 9, 51, 157, 310, 10, 21, 11, 7, 153, 5, 3, 0, 2, 43, 2, 1, 4, 0, 3, 22, 11, 22, 10, 30,
   98, 21, 11, 25, 71, 55, 7, 1, 65, 0, 16, 3, 2, 2, 2, 26, 45, 28, 4, 28, 36, 7, 2, 27, 28, 53, 11, 21, 11, 18, 14,
@@ -62,7 +62,7 @@ var astralIdentifierStartCodes = [
   0, 2, 2, 2, 1, 2, 0, 3, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 1, 2, 0, 3, 3, 2, 6, 2, 3, 2, 3, 2, 0, 2, 9, 2, 16, 6, 2, 2,
   4, 2, 16, 4421, 42710, 42, 4148, 12, 221, 16355, 541
 ];
-var astralIdentifierCodes = [
+let astralIdentifierCodes = [
   509, 0, 227, 0, 150, 4, 294, 9, 1368, 2, 2, 1, 6, 3, 41, 2, 5, 0, 166, 1, 1306, 2, 54, 14, 32, 9, 16, 3, 46, 10,
   54, 9, 7, 2, 37, 13, 2, 9, 52, 0, 13, 2, 49, 13, 16, 9, 83, 11, 168, 11, 6, 9, 8, 2, 57, 0, 2, 6, 3, 1, 3, 2, 10,
   0, 11, 1, 3, 6, 4, 4, 316, 19, 13, 9, 214, 6, 3, 8, 112, 16, 16, 9, 82, 12, 9, 9, 535, 9, 20855, 9, 135, 4, 60, 6,