RFR(S): 8055004: Reduce allocation overhead in java.time.Period/Duration parse methods

Hi, can I have a review of this performance improvement to java.time.Period#parse and java.time.Duration#parse? bug: https://bugs.openjdk.java.net/browse/JDK-8055004 webrev: http://cr.openjdk.java.net/~redestad/8055004/webrev.0 The patch avoids String allocation through matcher.group(n) calls, utilizes recently added capability of parsing CharSequence offsets and improves on the rather awkward way fractions of a second was aligned to nanosecond precision in java.time.Duration. Microbenchmarks show a 1.2-1.5x throughput improvement in both cases. Thanks! /Claes