moved all string options to std::string

*****************************************************************
WARNING: this has the potential to break things in subtle ways...
         PLEASE TEST AND REPORT ANY WEIRDNESSES
*****************************************************************

HAVE_XXX defines.

This fixes three longstanding problems:

- the API was hard to use because some headers had HAVE_XXX ifdefs, so
  that cient codes had to know how the lib was compiled to compile
  themselves

- we had to do make clean after each ./configure, which erased too
  much (e.g. most of contrib)

- make depend could include unwanted stuff since it redefined FLAGS

that the 2 steps are orthogonal
* added full-hexa subdivision algo

- fix bb computation to avoid model jumping around when adding points in z=0 plane
- pass interpol matrices as ref

There's no new functionality for now: PLEASE TEST THAT EVERYTHING
WORKS AS IT USED TO BEFORE.

reparametrization through harmonic maps enhanced

* add lc_extend_from_boundary in GUI

- removed every "throw;", i.e., every throw that did not throw an actual exception.
  throw wihout args should ONLY be used in a catch{} to re-throw the same exception
  (for it to be handled in another catch clause)

- introduced GmshMessage callback class so that clients can easily implement
  their own message handling (see example in driverOCC.cpp)

* implemented first rough draft of VTK mesh writer

  did in high
* added mesh generation error log summary
* removed Parallel subdir (this is now handled by the message class)
* removed Box subdir and consolidated batch processing in a single
  routine
* made List_T into a class
* reduced dependencies in Pview*.h so we can eventually add the post-pro
  interface to the public API

when creating single lib (boundarylayer.cc exists in netgen)

untabify

- new GmshInitialize(argc, argv) and GmshFinalize() for library version,
  now also used throughout

- GModel::mesh(dimension)

We now have a simple API to do basic stuff. We'll interface more as we go (optimize, adapt, etc.).

#include <stdio.h>
#include <gmsh/Gmsh.h>
#include <gmsh/GModel.h>
#include <gmsh/MElement.h>

int main(int argc, char **argv)
{
  GmshInitialize(argc, argv);
  GModel *m = new GModel();
  m->readGEO("./tutorial/t5.geo");
  m->mesh(3);
  for(GModel::riter it = m->firstRegion(); it != m->lastRegion(); ++it){
    printf("volume %d contains %d elements:\n", (*it)->tag(), (*it)->getNumMeshElements());
    for(unsigned int i = 0; i < (*it)->getNumMeshElements(); i++)
      printf(" %d", (*it)->getMeshElement(i)->getNum());
    printf("\n");
  }
  m->writeMSH("test.msh");
  m->writeUNV("test.unv");
  GmshFinalize();
}

introduce notion of entities in PViewData (in prepa for gmodel stuff)

- clean up GModel API (xxByTag -> getXx, numXx -> getNumXxes, ...)

allow multiple optimization passes

move random seed init in GenerateMesh

start reducing header pollution (removed Gmsh.h + cleaned up GModel & co)