quantity.example: comments

quantity.example: add illustrative example for scalars and a volterra integral of 2nd kind for 2x2 kernels

new: misc.getfield for hierarchical structs, example: myStruct.topLevel.lowerLevel.data == misc.getfield(myStruct, 'topLevel.lowerLevel.data')

- added methods imag() and real()
quantity.Symbolic:
- new method combineGridGridNameVariable() to avoid duplication of code in mathematical operations (mtimes, plus)

quantity: added 'stable' option to unique()-calls. Hence, the order of gridNames is not sorted but remains unchanged in most cases.

- added cumInt() that behaves as Discrete method but only calls int() of Symbolic
- fixed plus for quantities with different variables
- deleted minus since minus in parent class Discrete calls plus() of Symbolic, hence an additional implementation of minus in Symbolic was not necessary.

- previously for gridNames with more than one char, int was called recursivley (for 'zeta', int was called for ('z', 'e', 't', 'a'). Fixed that.
- yet, int does not consider inputs for integral bounds that do not coincide with the bounds of the grid. hence now a assertion informs about that problem if different bounds specified by inputs.

- fixed infinite loop in mtimes()

quantity.Discrete & .Symbolic:
- renamed variables in isConstant() to improve readability

quantity.Discrete & quantity.Symbolic: plus and minus now support quantity and numeric arrays of same size.

- plot() added option to hide array indices in title >> 'titleWithIndex', false
- l2norm() calculate quadratic norm

quantity.Discrete.gridOf() if quantity has no grid that coincides with the input gridName, then an [] is returned.

- solveAlgebraic: adjusted to change of changeGrid from call-by-reference to call-by-value
- diff(): now supports specification of various variables for which the derivative should be applied. Ensured consistency with Symbolic. Maybe a more elegant use of gradient() is possible.
- unittests: adjusted for now behavior of diff()

quantity.Symbolic bugfixes:
- diff(): now supports specification of various variables for which the derivative should be applied. Ensured consistency with Discrete.
- unittests: adjusted for now behavior of diff()

Changed implementation of integration for "Discretes". The input arguments are now consitent with the matlab "int" function.