Adding various new mesh prototypes

For visualization check emails with Christoph Geuzaine.
Also, Coherence; and Mesh.Algorithm = 5; are two very powerful options.

Meshes/disk_ball.geo

+SetFactory("OpenCASCADE");
+Mesh.Algorithm = 5; // Necessary to avoid problems with small lc at VIn
+Disk(1) = {0, 0, 0, 4};
+
+Field[5] = Ball;
+Field[5].Radius = 0.5;
+Field[5].VIn = 0.01;
+Field[5].VOut = 0.05;
+Background Field = 5;
\ No newline at end of file

Meshes/disk_double_gauss.geo

+SetFactory("OpenCASCADE");
+Mesh.Algorithm = 5; // Necessary to avoid problems with small lc
+Disk(1) = {0, 0, 0, 4};
+
+Physical Surface("surfacedomain") = {1};
+
+Field[3] = MathEval;
+Field[3].F = ".35 - (.335)*exp(-(1./0.05) *((sqrt(x*x+y*y+z*z)-0.8))*((sqrt(x*x+y*y+z*z)-0.8)))";
+Field[4] = MathEval;
+Field[4].F = ".35 - (.335)*exp(-(1./0.05) *((sqrt(x*x+y*y+z*z)-1.1))*((sqrt(x*x+y*y+z*z)-1.1)))";
+
+Field[5] = Min;
+Field[5].FieldsList={3,4};
+Background Field = 5;
\ No newline at end of file

Meshes/disk_gauss.geo

+SetFactory("OpenCASCADE");
+Disk(1) = {0, 0, 0, 4};
+
+Physical Surface("surfacedomain") = {1};
+
+Field[3] = MathEval;
+Field[3].F = ".5 - (.5-0.01)*exp(-(1./0.1) *((sqrt(x*x+y*y)-1))*((sqrt(x*x+y*y)-1)))";
+
+Mesh.Algorithm = 5; // This is necessary to avoid irregularities of Gaussian
+Background Field = 3;

Meshes/sphere_bool_diff.geo

+// NOT TESTED, POTENTIAL ISSUES
+SetFactory("OpenCASCADE");
+Sphere(1) = {0, 0, 0, 0.8, -Pi/2, Pi/2, 2*Pi};
+Sphere(2) = {0, 0, 0, 1., -Pi/2, Pi/2, 2*Pi};
+Sphere(3) = {0, 0, 0, 2, -Pi/2, Pi/2, 2*Pi};
+BooleanDifference(4) = { Volume{2}; Delete; }{ Volume{1};};
+
+lcar1 = .35;
+lcar2 = .15;
+lcar3 = .01;
+Physical Surface("surfacedomain") = {3};
+Physical Volume("volumedomain") = {3};
+
+Characteristic Length{ PointsOf{ Volume{4}; } } = lcar3;
+Characteristic Length{ PointsOf{ Volume{1}; } } = lcar2;
+Characteristic Length{ PointsOf{ Volume{3}; } } = lcar1;
+
+Coherence;
\ No newline at end of file

Meshes/sphere_concentric.geo

+// NOT TESTED, POTENTIAL ISSUES
+SetFactory("OpenCASCADE");
+Sphere(1) = {0, 0, 0, 0.8, -Pi/2, Pi/2, 2*Pi};
+Sphere(2) = {0, 0, 0, 0.95, -Pi/2, Pi/2, 2*Pi};
+Sphere(3) = {0, 0, 0, 1.05, -Pi/2, Pi/2, 2*Pi};
+Sphere(4) = {0, 0, 0, 2, -Pi/2, Pi/2, 2*Pi};
+
+lcar1 = .45;
+lcar2 = .35;
+lcar3 = .04;
+Physical Surface("surfacedomain") = {4};
+//+
+Physical Volume("volumedomain") = {1,2,3,4};
+//+
+Characteristic Length{ PointsOf{ Volume{1}; } } = lcar1;
+Characteristic Length{ PointsOf{ Volume{2}; } } = lcar3;
+Characteristic Length{ PointsOf{ Volume{3}; } } = lcar3;
+Characteristic Length{ PointsOf{ Volume{4}; } } = lcar1;
+
+
+Coherence; //Necessary to connect all volumes/make mesh coherent
\ No newline at end of file

Meshes/sphere_gauss.geo

+SetFactory("OpenCASCADE");
+Sphere(1) = {0, 0, 0, 4, -Pi/2, Pi/2, 2*Pi};
+
+Physical Surface("surfacedomain") = {1};
+Physical Volume("volumedomain") = {1};
+
+Field[3] = MathEval;
+Field[3].F = "1.0 - (1.0-0.0025)*exp(-(1./0.4) *((sqrt(x*x+y*y+z*z)-0.15))*((sqrt(x*x+y*y+z*z)-0.15)))";
+
+Background Field = 3;
\ No newline at end of file