Add trivial != operators to various HilbertIndices objects.
Fix small documentation issue in libHilbert.
Print (x,y,z) coords for HilbertIndices that are not found.
Merge branch 'hilbert_debug'
Update traffic.
Update plots.
Update references.
DenseVectorBase::empty(), const T & operator()

empty() adds a missing STL-like function.

Returning a reference in both const and non-const accessors lets us
easily pull out a valid T* for use in other APIs.
PetscVector<T>::insert specializations

If we have a whole N-vector of values to add, we can add them all with
1 PETSc call instead of N.
Refactor NumericVector::insert()

Add an insert() overload that takes const T* input; this now forms the
underlying implementation of several other overloads.

Move common insert() overloads into NumericVector rather than defining
them redundantly in subclasses; use a using declaration when necessary
to prevent this from leading to hidden overloads.

Make those less-raw overloads inline and non-virtual; particular
subclasses should find it sufficient to overload the T* method.
Merge pull request #411 from roystgnr/performance_tweaks

PetscVector::insert performance tweaks
Store node pointers in Side

This means that get_node(), point() can now be much simpler and can be
inline instead of virtual.
Avoid allocation in dof_indices()

We may need a temporary vector in the TRI3SUBDIVISION case but we can
avoid it in the common case
Close up PerfLog on every function return

This fixes a miscellaneous_ex11 bug with PerfLog enabled
NumericVector::get refactoring

Added an API for get(T*), and refactored the get(vector<T>) API to be
an inline wrapper for it.
Reduce some variable scope
Merge nested if statements
Cache some accessor results

This may be overkill, but I don't think it's *theoretically* overkill;
we call non-inline functions in between these accessor calls and so
even though we can be sure the results haven't changed, the compiler
probably can't.
Only assert scalars are scalars in dbg mode
Cache SCALAR dof index locations in DofMap