Updated to Box2D 2.3.1

Closes #39
Updated to Box2D 2.3.2 (trunk)

This version is not tagged yet, but contains one more memory.h include
fix.
Merge pull request #45 from bjorn/master

Synchronization simplifications
Changed position of header guard for consistency
fix linker error due to excessive onRotationChanged slot
Merge pull request #46 from folibis/fixes

Fix linker error due to excessive onRotationChanged slot
Removed a source from the static pri that has been removed from the tree
Merge pull request #48 from kenvandine/static_pri

Removed a source from the static pri that has been removed from the tree
Install plugin in a version directory to allow parallel installable versions
dropped unneeded check for importPath
Update examples
Fix Body::angularVelocity() return value
Merge pull request #50 from folibis/morefixes

Fix Body::angularVelocity() return value
turn hard-coded 'pixelsPerMeter' into Box2DWorld's property
Merge pull request #51 from ElderOrb/master

turn hard-coded 'pixelsPerMeter' into Box2DWorld's property
Merge pull request #49 from kenvandine/parallel_installable

Install plugin in a versioned directory to allow parallel installable versions
Merge pull request #47 from folibis/examples

Update examples
Added profiling of synchronization and signal emission
Reintroduced qFuzzyCompare for synchronization

Avoiding updates to body position and rotation when the change is very
small seems to reduce the synchronization time significantly when there
is a large amount of awake bodies.