add enum baudrates (#376)

* add enum baudrates

fixes perceived limitation of available baud rates https://github.com/Microsoft/pxt/issues/1752

* correct block comment

* comma correction and remove trailing space

That will teach me just to do cut and paste via github web interface :(

* without running pxt buildtarget

libs/core/enums.d.ts

@@ -443,8 +443,26 @@ declare namespace led {
     declare enum BaudRate {
     //% block=115200
     BaudRate115200 = 115200,
+    //% block=57600
+    BaudRate57600 = 57600,
+    //% block=38400
+    BaudRate38400 = 38400,
+    //% block=28800
+    BaudRate28800 = 28800,
+    //% block=19200
+    BaudRate19200 = 19200,
+    //% block=14400
+    BaudRate14400 = 14400,
     //% block=9600
     BaudRate9600 = 9600,
+    //% block=4800
+    BaudRate4800 = 4800,
+    //% block=2400
+    BaudRate2400 = 2400,
+    //% block=1200
+    BaudRate1200 = 1200,
+    //% block=300
+    BaudRate300 = 300,
     }