get rid of gb_math and create matrices from scratch

src/math.zig

@@ -0,0 +1,24 @@
+pub const F32x4 = @Vector(4, f32);
+
+/// Matrix type
+pub const Mat = [4]F32x4;
+
+/// Identity matrix
+pub fn identity() Mat {
+    return .{
+        .{ 1.0, 0.0, 0.0, 0.0 },
+        .{ 0.0, 1.0, 0.0, 0.0 },
+        .{ 0.0, 0.0, 1.0, 0.0 },
+        .{ 0.0, 0.0, 0.0, 1.0 },
+    };
+}
+
+pub fn ortho2d(left: f32, right: f32, bottom: f32, top: f32) Mat {
+    var mat = identity();
+    mat[0][0] = 2 / (right - left);
+    mat[1][1] = 2 / (top - bottom);
+    mat[2][2] = -1.0;
+    mat[3][0] = -(right + left) / (right - left);
+    mat[3][1] = -(top + bottom) / (top - bottom);
+    return mat;
+}