Building igl statically and moving to the dep scripts

Fixing dep build script on Windows and removing some warnings.

Use bundled igl by default.

Not building with the dependency scripts if not explicitly stated. This way, it will stay in
Fix the libigl patch to include C source files in header only mode.

src/libigl/igl/is_stl.cpp

@@ -0,0 +1,64 @@
+#include "is_stl.h"
+#include <string>
+IGL_INLINE bool igl::is_stl(FILE * stl_file, bool & is_ascii)
+{
+
+  //      solid?
+  //   YES      NO
+  //   /         if .stl, definitely binary
+  //  /
+  // perfect size?
+  //      YES     NO
+  //
+  const auto perfect_size = [](FILE * stl_file)->bool
+  {
+    //stl_file = freopen(NULL,"rb",stl_file);
+    // Read 80 header
+    char header[80];
+    if(fread(header,sizeof(char),80,stl_file)!=80)
+    {
+      return false;
+    }
+    // Read number of triangles
+    unsigned int num_tri;
+    if(fread(&num_tri,sizeof(unsigned int),1,stl_file)!=1)
+    {
+      return false;
+    }
+    fseek(stl_file,0,SEEK_END);
+    int file_size = ftell(stl_file);
+    fseek(stl_file,0,SEEK_SET);
+    //stl_file = freopen(NULL,"r",stl_file);
+    return (file_size == 80 + 4 + (4*12 + 2) * num_tri);
+  };
+  // Specifically 80 character header
+  char header[80];
+  char solid[80];
+  is_ascii = true;
+  bool f = true;
+  if(fread(header,1,80,stl_file) != 80)
+  {
+    f = false;
+    goto finish;
+  }
+
+  sscanf(header,"%s",solid);
+  if(std::string("solid") == solid)
+  {
+    f = true;
+    is_ascii = !perfect_size(stl_file);
+  }else
+  {
+    is_ascii = false;
+    f = perfect_size(stl_file);
+  }
+finish:
+  rewind(stl_file);
+  return f;
+}
+
+IGL_INLINE bool igl::is_stl(FILE * stl_file)
+{
+  bool is_ascii;
+  return is_stl(stl_file,is_ascii);
+}