Re-implement functions and functions form R^n into R^m

[rafaelrojasmiliani]

At the commit 8b53d24, functions are only intended to represent curves. However, in order to reresent maps between manifolds we can expand this type into maps from R^n into R^m.

• Define an abstract class called domain with the following pure virtual methods
  • With equal operator
  • with "contain" method which accept a point
  • with "contain" method which accepts another domain
  • with dimension method "dim"
  • make is inheritance helper
  • clone, move_clone
• redefine the base function class
  • it has a domain as a member
  • Modify its value member. Now value should accept an array of elements of its domain (Vector<double, N, 1>)
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