Clean up

* Remove shebangs referring to python2.6
* Remove copylight lines
* Rename _core.pyx to _levmar.pyx
Use standard exceptions and UserWarning
Remove a convenient class Output
Remove examples/
Refactor

* Split a single function levmar() to functions with different constraints
* Remove _LMConstraints and its relatives
* Box constraints must a sequence of 2-tuples
* Specify linear constraints as a tuple of a 2d array and 1d array.
Remove dependency on np.distutils
Add examples/
Merge branch 'refactoring' into develop