minor update manual
fix vehicle demo (heightfield is broken, when using very large scaling factor)
add btConeShape serialization, see Issue 725
add btGearConstraint get/set, see Issue 685 and Issue 671

git-svn-id: http://bullet.googlecode.com/svn/trunk@2665 08e121b0-ae19-0410-a57b-3be3395fd4fd
refactor constraint serialization, so that double precision is maintained,
changes are backwards compatible (btBulletWorldImporter can load old .bullet files)
but not forwards compatible (constraints in new .bullet files are ignored/unrecognized by old Bullet SDK)
This commit is for Issue 734. Some more work needs to be done for btGImpactMeshShapeDoubleData and thus btStridingMeshInterfaceDoubleData and btMeshPartDoubleData

git-svn-id: http://bullet.googlecode.com/svn/trunk@2666 08e121b0-ae19-0410-a57b-3be3395fd4fd
update serialization structures

git-svn-id: http://bullet.googlecode.com/svn/trunk@2667 08e121b0-ae19-0410-a57b-3be3395fd4fd