Make lzma.{encode,decode}_filter_properties private.

These functions were originally added to support LZMA compression in the zipfile
module, and are not of interest for the majority of users.

They can be made public in 3.4 if there is user interest, but in the meanwhile,
I've opted to present a smaller, simpler API for the module's initial release.
diff --git a/Modules/_lzmamodule.c b/Modules/_lzmamodule.c
index 6720d4c..b482a77 100644
--- a/Modules/_lzmamodule.c
+++ b/Modules/_lzmamodule.c
@@ -1097,19 +1097,16 @@
 }
 
 
-PyDoc_STRVAR(encode_filter_properties_doc,
-"encode_filter_properties(filter) -> bytes\n"
+PyDoc_STRVAR(_encode_filter_properties_doc,
+"_encode_filter_properties(filter) -> bytes\n"
 "\n"
 "Return a bytes object encoding the options (properties) of the filter\n"
 "specified by *filter* (a dict).\n"
 "\n"
-"The result does not include the filter ID itself, only the options.\n"
-"\n"
-"This function is primarily of interest to users implementing custom\n"
-"file formats.\n");
+"The result does not include the filter ID itself, only the options.\n");
 
 static PyObject *
-encode_filter_properties(PyObject *self, PyObject *args)
+_encode_filter_properties(PyObject *self, PyObject *args)
 {
     PyObject *filterspec;
     lzma_filter filter;
@@ -1117,7 +1114,7 @@
     uint32_t encoded_size;
     PyObject *result = NULL;
 
-    if (!PyArg_ParseTuple(args, "O:encode_filter_properties", &filterspec))
+    if (!PyArg_ParseTuple(args, "O:_encode_filter_properties", &filterspec))
         return NULL;
 
     if (parse_filter_spec(&filter, filterspec) == NULL)
@@ -1146,24 +1143,21 @@
 }
 
 
-PyDoc_STRVAR(decode_filter_properties_doc,
-"decode_filter_properties(filter_id, encoded_props) -> dict\n"
+PyDoc_STRVAR(_decode_filter_properties_doc,
+"_decode_filter_properties(filter_id, encoded_props) -> dict\n"
 "\n"
 "Return a dict describing a filter with ID *filter_id*, and options\n"
-"(properties) decoded from the bytes object *encoded_props*.\n"
-"\n"
-"This function is primarily of interest to users implementing custom\n"
-"file formats.\n");
+"(properties) decoded from the bytes object *encoded_props*.\n");
 
 static PyObject *
-decode_filter_properties(PyObject *self, PyObject *args)
+_decode_filter_properties(PyObject *self, PyObject *args)
 {
     Py_buffer encoded_props;
     lzma_filter filter;
     lzma_ret lzret;
     PyObject *result = NULL;
 
-    if (!PyArg_ParseTuple(args, "O&y*:decode_filter_properties",
+    if (!PyArg_ParseTuple(args, "O&y*:_decode_filter_properties",
                           lzma_vli_converter, &filter.id, &encoded_props))
         return NULL;
 
@@ -1187,10 +1181,10 @@
 static PyMethodDef module_methods[] = {
     {"is_check_supported", (PyCFunction)is_check_supported,
      METH_VARARGS, is_check_supported_doc},
-    {"encode_filter_properties", (PyCFunction)encode_filter_properties,
-     METH_VARARGS, encode_filter_properties_doc},
-    {"decode_filter_properties", (PyCFunction)decode_filter_properties,
-     METH_VARARGS, decode_filter_properties_doc},
+    {"_encode_filter_properties", (PyCFunction)_encode_filter_properties,
+     METH_VARARGS, _encode_filter_properties_doc},
+    {"_decode_filter_properties", (PyCFunction)_decode_filter_properties,
+     METH_VARARGS, _decode_filter_properties_doc},
     {NULL}
 };