Add nlopt optimizer
Add nlopt dependency setting for CPACK, Travis-CI, and debian packaging
Build and install nlopt from source in Travis-CI test

The Ubuntu version of Travis-CI is 12.04 LTS but debian package for nlopt is not deliverd in the version.
Try to build nlopt in Travis-CI
Add reference for the optimization example problem
Try to build nlopt in Travis-CI
Try to build nlopt in Travis-CI
Try to build nlopt in Travis-CI
Remove custom cmake keyword

build_warning --> message
Add -fPIC build option for nlopt
Add -fPIC build option to CPPLAGS for nlopt
Fix make command for nlopt
Fix make command for nlopt
Update Changelog.md
Modify optimization interface to be more general
Add initial implementation for `ipopt` solver
Install coinor-libipopt-dev in Travis-CI test
Rollback installing coinor-libipopt-dev in Travis-CI test

The debian package from apt-get does not work
Add reference to issue #153 for ipopt test
Fix style and add copyright to testForwardKinematics.cpp