make most headers private

src/mbgl/geometry/fill_buffer.cpp

@@ -0,0 +1,13 @@
+#include <mbgl/geometry/fill_buffer.hpp>
+
+#include <mbgl/platform/gl.hpp>
+
+#include <climits>
+
+using namespace mbgl;
+
+void FillVertexBuffer::add(vertex_type x, vertex_type y) {
+    vertex_type *vertices = static_cast<vertex_type *>(addElement());
+    vertices[0] = x;
+    vertices[1] = y;
+}