Corrected an exception message.
Corrected an include guard name.
First (very preliminary!) version of the code for evaluating potentials with ACA.
Potential-operator ACA assembly should now work for vector potentials.
Fixed H-matrix Postscript output for rectangular matrices.
Added explicit instantiation of operator+ for BoundaryOperators.
Added a componentCount() virtual function to PotentialOperator.

(Source-incompatible change, but users are not very likely to derive
new classes from PotentialOperator.)
Refactored the interface of PotentialOperator related to caching of potential
operator matrices.
Extracted AcaOptions into its own file.
Extended EvaluationOptions with field such as evaluationMode (dense/ACA).
Mentioned the requirement of linearity of elementary potential operators.
ElementaryPotentialOperator::evaluateAtPoints() now respects assembly mode.
Slightly reformatted elementary_potential_operator.cpp and added a
"not implemented" error message.
Implemented accessor methods from AssembledPotentialOperator.
Partially adapted Python wrappers to the new PotentialOperator interface.
Added an input typemap for shared pointers to constant Armadillo arrays.
Added a method size() to IndexPermutation.
Extracted common parts of weak form and potential operator ACA assembly
into a separate function.

Added a function to dump dense mblocks.
Extracted code common for various local assemblers into a separate utility
struct.
Potential evaluation can now be done with variable quadrature order.