Fix the automatic detection of the include directory for Python 3.10 (#44)

* Fix the automatic detection of the include directory for Python 3.10

- `sysconfig` has been supported since 3.2
- Since we support only Python > 3.6,  we use `import sysconfig; print(sysconfig.get_path('include'))` to get the include path.

python_configure.bzl

diff --git a/python_configure.bzl b/python_configure.bzl
index bb505c7..8241368 100644
--- a/python_configure.bzl
+++ b/python_configure.bzl
@@ -246,19 +246,14 @@
 
 def _get_python_include(repository_ctx, python_bin):
     """Gets the python include path."""
-    python_lib = repository_ctx.os.environ.get(_PYTHON_LIB_PATH)
-    if python_lib != None:
-        return python_lib
     result = _execute(
         repository_ctx,
         [
             python_bin,
             "-c",
-            "from __future__ import print_function;" +
-            "from distutils import sysconfig;" +
-            "print(sysconfig.get_python_inc())",
+            "import sysconfig; print(sysconfig.get_path('include'))",
         ],
-        error_msg = "Problem getting python include path.",
+        error_msg = "Problem getting python include path for Python version " + str(version),
         error_details = ("Is the Python binary path set up right? " +
                          "(See ./configure or " + _PYTHON_BIN_PATH + ".) " +
                          "Is distutils installed?"),