fail gracefully with a bad user im-/exporter; improve docs slightly

Author: briantoby

GSASII/GSASIIfiles.py

@@ -636,8 +636,9 @@ def LoadImportRoutines(prefix, errprefix=None, traceback=False):
                     reader.longFormatName = '(user supplied) ' + reader.longFormatName
                     if reader.UseReader:
                         readerlist.append(reader)
-        except ImportError as msg:
-            print(f'Failed to import importer {f} with error\n{msg}')
+        except Exception as msg:
+            G2Print(f'\nImporter init: error with importer file {f!r}')
+            G2Print ('Error message: {}\n'.format(msg))
     return readerlist
 
 def LoadExportRoutines(parent, usetraceback=False):
@@ -694,7 +695,7 @@ def LoadExportRoutines(parent, usetraceback=False):
             # not sure if I want to do this or not
             sys.modules[f"GSASII.userexports.{nam}"] = module
         except Exception as exc:
-            G2Print (f'\nExport init: Error with file {f}')
+            G2Print (f'\nExport init: Error with exporter file {f!r}')
             G2Print ('Error message: {}\n'.format(exc))
             if usetraceback:
                 import traceback

docs/source/exports.rst

@@ -25,9 +25,14 @@ be written.
 A file containing one or more export routine can be placed
 either in the ``GSASII/exports`` directory (which requires
 modification of the ``__init__.py`` file or the file can be placed in
-the ``~/.GSASII/exports`` directory.   
+the ``~/.GSASII/exports`` directory.
+(Note that ``~`` here is translated to the 
+user's home directory; for Windows this is usually taken from the
+USERPROFILE setting or a combination of HOMEPATH and HOMEDRIVE,
+so this directory will usually have form
+``C:\\Users\\YourUsername\\.GSASII\\exports``.
 The next time GSAS-II is started,
-the file will loaded when the GSAS-II files are read by the Python and
+the file will be loaded with all the other GSAS-II files and
 the new data format will appear in the appropriate exporter menu. 
 
 .. _export_routines: 

docs/source/imports.rst

@@ -41,11 +41,17 @@ named with the appropriate file name prefix:
 This file can be placed
 either in the ``GSASII/imports`` directory (which requires
 modification of the ``__init__.py`` file or the file can be placed in
-the ``~/.GSASII/imports`` directory.   The importer file may contain a
-single import class or several. 
+the ``~/.GSASII/imports`` directory.
+(Note that ``~`` here is translated to the 
+user's home directory; for Windows this is usually taken from the
+USERPROFILE setting or a combination of HOMEPATH and HOMEDRIVE,
+so this directory will usually have form
+``C:\\Users\\YourUsername\\.GSASII\\imports``.
 The next time GSAS-II is started,
-the file will loaded when the GSAS-II files are read by the Python and
+the file will be loaded with all the other GSAS-II files and
 the new data format(s) will appear in the appropriate importer menu. 
+The importer file may contain a
+single importer class or several. 
 
 Importers are documented below, separated by type. Importers tend to
 be fairly simple files, where many are in the range of 50-100 lines,