Some fixes. Rollback draft for shift.
On branch rollback
modified:   lib/train.js
modified:   package.json
v 2.8.0. ok
Fixed bug in #shift.
On branch rollback
modified:   lib/train.js
modified:   package.json
modified:   test/indexOf-test.js
modified:   test/xpush-test.js
v 2.9.0.
Added rollback mechanism and rollback tests.
Fixed #concat and #xconcat with no arguments.
On branch rollback
modified:   Readme.md
modified:   lib/train.js
modified:   package.json
modified:   test/indexOf-test.js
new file:   test/rollBack-mixed-test.js
new file:   test/rollBack-pop-test.js
new file:   test/rollBack-shift-test.js
v 2.9.1.
Some minor fixes in the Readme, package.json and tests.
On branch rollback
modified:   .travis.yml
modified:   Readme.md
modified:   package.json
modified:   test/rollBack-mixed-test.js
modified:   test/rollBack-pop-test.js
modified:   test/rollBack-shift-test.js
v 2.9.2.
Added #rollUp and #rollBack signatures to the Readme.
On branch rollback
modified:   Readme.md
modified:   package.json
2.9.3.
Corrected Readme.
On branch rollback
modified:   Readme.md
modified:   package.json
Merge branch 'rollback'
v 3.0.0.
Added rollback mechanism, with #rollUp() and #rollBack().
Some readme and code fixes.
Added tests.
On branch master
modified:   package.json