[master] RFR: Only include Mark Word when required

[Julian Waters]

WIP

Discussion: https://bugs.openjdk.java.net/browse/JDK-8198331

Current goals and dependencies (To help keep track)
- [x] 2 bit identity Hash Code
- [ ] Elimination of locking from the Mark Word entirely (Hopefully)
- [ ] 5 bit GC section (4 bit object age, 1 bit forwarding state)
- [ ] No Mark Word in header until required
- [ ] Support and optimizations for objects guaranteed to not have a Mark Word (May depend on Valhalla for the GC section)

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Commit messages:
 - Initial Commit

Changes: https://git.openjdk.java.net/lilliput/pull/47/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lilliput&pr=47&range=00
  Stats: 6 lines in 2 files changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/47.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/47/head:pull/47

PR: https://git.openjdk.java.net/lilliput/pull/47