Update date documentation (#64)

Adding functionality from AssemblyScript/assemblyscript#1768

Author: ColinEberhardt

src/stdlib/date.md

@@ -6,7 +6,7 @@ description: Represents timestamps.
 
 Represents timestamps.
 
-The Date API is still preliminary and requires importing the `Date` object from the host \(as `Date`\).
+The Date API is still preliminary with only a subset of properties and methods implemented. Note that getting the current date, via `Date.now`, requires importing the `Date` object from the host \(as `Date`\).
 
 ## Constructor
 
@@ -20,7 +20,7 @@ The Date API is still preliminary and requires importing the `Date` object from
 * ```ts
   function now(): i64
   ```
-  Returns the current UTC timestamp in milliseconds.
+  Returns the current UTC timestamp in milliseconds. To use this function you must import the `Date` object from the host \(as `Date`\).
 
 * ```ts
   function UTC(
@@ -34,6 +34,11 @@ The Date API is still preliminary and requires importing the `Date` object from
   ): i64
   ```
   Returns the UTC timestamp in milliseconds of the specified date.
+  
+* ```ts
+   function fromString(dateTimeString: string): Date 
+  ```
+  Creates a Date object from an ISO 8601 formatted string.
 
 ## Instance members
 
@@ -46,3 +51,79 @@ The Date API is still preliminary and requires importing the `Date` object from
   function setTime(value: i64): i64
   ```
   Sets the UTC timestamp of this date in milliseconds and returns the timestamp.
+  
+* ```ts
+  function getUTCFullYear(): i32
+  ```
+  Gets the full year according to universal time.
+
+* ```ts
+  function setUTCFullYear(value: i32): i32
+  ```
+  Sets the full year according to universal time.
+
+* ```ts
+  function getUTCMonth(): i32
+  ```
+  Gets the (zero indexed) month according to universal time.
+
+* ```ts
+  function setUTCMonth(value: i32): i32
+  ```
+  Sets the (zero indexed) month according to universal time.
+  
+* ```ts
+  function getUTCDate(): i32
+  ```
+  Gets the day of the month according to universal time.
+
+* ```ts
+  function setUTCDate(value: i32): i32
+  ```
+  Sets the day of the month according to universal time.
+  
+* ```ts
+  function getUTCHours(): i32
+  ```
+  Gets the hour according to universal time.
+
+* ```ts
+  function setUTCHours(value: i32): i32
+  ```
+  Sets the hour according to universal time.
+  
+* ```ts
+  function getUTCMinutes(): i32
+  ```
+  Gets the minute according to universal time.
+
+* ```ts
+  function setUTCMinutes(value: i32): i32
+  ```
+  Sets the minute according to universal time.
+  
+* ```ts
+  function getUTCSeconds(): i32
+  ```
+  Gets the second according to universal time.
+
+* ```ts
+  function setUTCSeconds(value: i32): i32
+  ```
+  Sets the second according to universal time.
+  
+* ```ts
+  function getUTCMilliseconds(): i32
+  ```
+  Gets the millisecond according to universal time.
+
+* ```ts
+  function setUTCMilliseconds(value: i32): i32
+  ```
+  Sets the millisecond according to universal time.
+ 
+* ```ts
+  function toISOString(): string
+  ```
+  Returns the a string in simplified extended ISO 8601 format.
+