Access to integrals values via python

[mfherbst]

One should probably extend the python interface. Some ideas:

• Have a class Integrals, which is constructed using a PamMap specifying the details
• The class should have a get function which allows to specify a string describing the integrals
  (be flexible here) and some kwargs regarding derivative order and so on
• Perhaps also map frequent cases to actual attributes, e.g. overlap
• First the get function should only return numpy arrays
• Later lazyten expressions, which are potentially assembled on the C++ side.
• Notice that everything in a lazyten expression could be serialised to a PamMap including
  • Expression tree
  • Symbol name of the apply function (such that dlopen would find it)