Teach awyeah-api to handle ISO8601 timestamps with microsecond precision

This is a divergence from aws-api. The aws-api uses
java.text.SimpleDateFormat for timestamp parsing, and is unable to
parse timestamps with precision greater than milliseconds. (Attempting
to do so silently corrupts the timestamp. See aws-api commit
636a7af35b6f11c3b26eaa9aa47067ac5b312b20 for an example.)

awyeah-api uses java.time.format.DateTimeFormatter, which can parse
timestamps with up to nanosecond precision. We likely only need
microsecond precision given the samples I've seen, so add a formatter
than handles microsecond-precision ISO8601 timestamps.

src/com/grzm/awyeah/shape.clj

@@ -93,7 +93,8 @@
           (= "iso8601" timestampFormat)
           (parse-date* data
                        util/iso8601-date-format
-                       util/iso8601-msecs-date-format)
+                       util/iso8601-msecs-date-format
+                       util/iso8601-usecs-date-format)
           (int? data)
           (java.util.Date. (* 1000 ^int data))
           (double? data)
@@ -104,6 +105,7 @@
           (parse-date* data
                        util/iso8601-date-format
                        util/iso8601-msecs-date-format
+                       util/iso8601-usecs-date-format
                        util/rfc822-date-format))))
 
 ;; ----------------------------------------------------------------------------------------

src/com/grzm/awyeah/util.clj

@@ -58,6 +58,9 @@
 (def iso8601-msecs-date-format
   (date-format "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"))
 
+(def iso8601-usecs-date-format
+  (date-format "yyyy-MM-dd'T'HH:mm:ss.SSSSSS'Z'"))
+
 (def rfc822-date-format
   (date-format "EEE, dd MMM yyyy HH:mm:ss z"))