pybullet: add option to use NumPy to speed up, thanks to moof2k

option is disabled by default. When using cmake, use
cmake -DBUILD_PYBULLET=ON -DBUILD_PYBULLET_NUMPY=ON
then both testrender.py and testrender_np.py will work
without numpy only testrender.py works.
The numpy.reshape is likely a no-op when using numpy array,
so we could remove testrender_np.py...

See https://github.com/bulletphysics/bullet3/pull/774

build3/cmake/FindNumPy.cmake

@@ -0,0 +1,41 @@
+# Find the Python NumPy package
+# PYTHON_NUMPY_INCLUDE_DIR
+# PYTHON_NUMPY_FOUND
+# will be set by this script
+
+cmake_minimum_required(VERSION 2.6)
+
+if(NOT PYTHON_EXECUTABLE)
+  if(NumPy_FIND_QUIETLY)
+    find_package(PythonInterp QUIET)
+  else()
+    find_package(PythonInterp)
+    set(__numpy_out 1)
+  endif()
+endif()
+
+if (PYTHON_EXECUTABLE)
+  # Find out the include path
+  execute_process(
+    COMMAND "${PYTHON_EXECUTABLE}" -c
+            "from __future__ import print_function\ntry: import numpy; print(numpy.get_include(), end='')\nexcept:pass\n"
+            OUTPUT_VARIABLE __numpy_path)
+  # And the version
+  execute_process(
+    COMMAND "${PYTHON_EXECUTABLE}" -c
+            "from __future__ import print_function\ntry: import numpy; print(numpy.__version__, end='')\nexcept:pass\n"
+    OUTPUT_VARIABLE __numpy_version)
+elseif(__numpy_out)
+  message(STATUS "Python executable not found.")
+endif(PYTHON_EXECUTABLE)
+
+find_path(PYTHON_NUMPY_INCLUDE_DIR numpy/arrayobject.h
+  HINTS "${__numpy_path}" "${PYTHON_INCLUDE_PATH}" NO_DEFAULT_PATH)
+
+if(PYTHON_NUMPY_INCLUDE_DIR)
+  set(PYTHON_NUMPY_FOUND 1 CACHE INTERNAL "Python numpy found")
+endif(PYTHON_NUMPY_INCLUDE_DIR)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(NumPy REQUIRED_VARS PYTHON_NUMPY_INCLUDE_DIR
+                                        VERSION_VAR __numpy_version)