update user documentation for 3.1.2

docs/doxygen-user/Doxyfile

docs/doxygen-user/EXIF_parser_page.dox

docs/doxygen-user/README.txt

docs/doxygen-user/android_analyzer.dox

docs/doxygen-user/archive_extractor.dox

docs/doxygen-user/case_management.dox

docs/doxygen-user/content_viewer.dox

docs/doxygen-user/data_sources.dox

docs/doxygen-user/directory_tree.dox

docs/doxygen-user/e01_verifier.dox

docs/doxygen-user/email_parser.dox

docs/doxygen-user/extension_mismatch.dox

docs/doxygen-user/file_search.dox

docs/doxygen-user/filetype.dox

docs/doxygen-user/footer.html

docs/doxygen-user/hashdb_lookup.dox

docs/doxygen-user/image_viewer.dox

docs/doxygen-user/images/EXIF-tree.PNG

docs/doxygen-user/images/add-data-source.PNG

docs/doxygen-user/images/android_analyzer_output.PNG