Merge pull request #441 from enthought/add_fetch_unpack_tool

FEAT: add simple unpack tool.
(cherry picked from commit 3e65bfb767cdff432763b18b9d833acf41425e30)
MAINT: update changelog for 4.8.1.
Merge pull request #449 from enthought/make_etag_context_thread_safe

Make etag context thread safe
(cherry picked from commit cea5987d1c746d77fc0c5935714b539cef765900)
Merge pull request #448 from enthought/fix_446

BUG: fix wrong interface definition for IAuth.
(cherry picked from commit 1dc9aeb6fc833753d628af57d557765adb0125a9)
MAINT: update changelog.
MAINT: release 4.8.1.