An ebuild for p4est [1]

This commit introduces an ebuild for the p4est library.

[1] http://www.p4est.org/

 "The p4est software library enables the dynamic management of a
  collection of adaptive octrees, conveniently called a forest of octrees.
  p4est is designed to work in parallel and scale to hundreds of thousands
  of processor cores."
An ebuild for deal.II [1]

This commit introduces an ebuild for the deal.II library.

[1] http://www.dealii.org/

 "deal.II is a C++ program library targeted at the computational solution of
  partial differential equations using adaptive finite elements. It uses
  state-of-the-art programming techniques to offer you a modern interface to the
  complex data structures and algorithms required."
Merge branch 'package-p4est'