This PR does two things:

1. I moved `package.json` into the root directory. Why? We are using `npx` from the `Makefile` which is executing usually under the root directory. If we install `node_modules` in `src/js` then these invocations don't see `node_modules` and install an extra copy of the packages. So we want `node_modules` in the root directory. node wants to put `node_modules` in the same directory as `package.json` hence I moved `package.json`. I also updated the build rules so that any recipe that uses `npx` has a dependency on `node_modules/.installed`.
2. We invoke `file_packager.py` from both the Makefile (in two places) and from `build_pkg`. There has been some drift in which options are applied in the two places. I extracted the common options and the task of locating the `file_packager.py` script into `tools/file_packager.sh`. I also shortened the make rules for `distutils.data` and `test.data` and made some minor updates to the dev docs about `file_packager.py`.
MAINT Improvements to node and file_packager invocations. This PR does two things:

1. I moved `package.json` into the root directory. Why? We are using `npx` from the `Makefile` which is executing usually under the root directory. If we install `node_modules` in `src/js` then these invocations don't see `node_modules` and install an extra copy of the packages. So we want `node_modules` in the root directory. node wants to put `node_modules` in the same directory as `package.json` hence I moved `package.json`. I also updated the build rules so that any recipe that uses `npx` has a dependency on `node_modules/.installed`.
2. We invoke `file_packager.py` from both the Makefile (in two places) and from `build_pkg`. There has been some drift in which options are applied in the two places. I extracted the common options and the task of locating the `file_packager.py` script into `tools/file_packager.sh`. I also shortened the make rules for `distutils.data` and `test.data` and made some minor updates to the dev docs about `file_packager.py`.
diff --git a/joblib/backports.py b/joblib/backports.py
index 7dd3df1..a49ef78 100644
--- a/joblib/backports.py
+++ b/joblib/backports.py
@@ -3,7 +3,6 @@ Backports of fixes for joblib dependencies
 """
 import os
 import time
-import ctypes
 import sys
 
 from distutils.version import LooseVersion
@@ -34,6 +33,8 @@ except ImportError:
 
 if os.name == 'nt':
     error_access_denied = 5
+    import ctypes
+
     try:
         from os import replace
     except ImportError:

diff --git a/joblib/backports.py b/joblib/backports.py
index 7dd3df1..a49ef78 100644
--- a/joblib/backports.py
+++ b/joblib/backports.py
@@ -3,7 +3,6 @@ Backports of fixes for joblib dependencies
 """
 import os
 import time
-import ctypes
 import sys
 
 from distutils.version import LooseVersion
@@ -34,6 +33,8 @@ except ImportError:
 
 if os.name == 'nt':
     error_access_denied = 5
+    import ctypes
+
     try:
         from os import replace
     except ImportError:
