Upgraded Guava to 14.0-rc2, #12
Pulled up component codec from render kits to StatePeerManager, #20

Collapsed IntegerIdComponentVisitor into StatePeerManager and made
state codecs use PeerManager for component codec.  The PeerManager is
provided to the render kit, and thus in turn the state codec, via a
hydration context parameter.

Removed now unused classes from symmetry-support-codec.
Moved PeerManager from symmetry-core to symmetry-api, #20

This centralises the main Symmetry API and further decommissions
symmetry-core.  It is also required to fix symmetry-jax-rs for the
changes introduced by this issue.
Updated symmetry-jax-rs to use PeerManager, #20

Now that render kits require a PeerManager within their hydration
context, updated ComponentWriter to obtain one via a JAX-RS @Provider.

Added a corresponding provider to symmetry-demo-jax-rs.
Refactored Codec to align with Guava's implementation, #14
Removed symmetry-support-codec now it's redundant, fixes #14

Issue #20 has further reduced the use of symmetry-support-codec, so much
so that it's remaining use for XML id encoding has been replaced with a
simple Guava Function.