- add iterators, begin/end, empty() methods for STL behaviour.
  Use standard algorithms where possible
     * std::fill, std::copy
     * std::min_element, std::max_element

- access methods consistent with other OpenFOAM containers:
     * data(), cdata(), uniform()

- Use ListPolicy to impose output line breaks

- Can recover matrix storage for re-use elsewhere.
  For example, to populate values with 2D i-j addressing and later
  release it as flat linear storage.

- construct/assign moveable

- added minMax() function for Matrix

- additional inplace +=, -=, *=, /= operations

- add named methods at() and rowData() to Matrix.
  Allows a better distinction between linear and row-based addressing

- low-level matrix solve on List/UList instead of Field