Merge pull request #132 from briandipalma/master

fix(Sequence.skip): returned collection was set to incorrect offset inde...
Stack

AKA single-LinkedList. This is the more simple of the persistent data structures and often quite useful. A great usage is in implementing an undo-stack!
Merge branch 'master' of github.com:facebook/immutable-js

Conflicts:
	dist/Immutable.min.js
Fix IE8 issue with Record and throw when setting an invalid key
Release 2.3.1
correct get for negative indices for take/skip
Fix negative index cases for Range and take/skip
Release 2.3.2
Fix lazy methods on ValuesSeq

get() and has() were unsafe since the point of ValuesSeq is to re-key based on incrementing index.

contains(), however, is safe.
Generalize `is` and make Cursor construction generic
generalize cursor construction, add updateIn to Cursor
Write test for sub-cursor. Fix editpath for sub-cursor
asMutable/asImmutable on Cursor
Cursor more explicitly supports Maps. Does not support scalars
MapCursor
Fix record.clear()
VectorCursor
Merge branch 'fix-record-clear' of github.com:zertosh/immutable-js into zertosh-fix-record-clear

Conflicts:
	dist/Immutable.min.js
Merge branch 'zertosh-fix-record-clear'
SetCursor