Don't absolutize count before passing it to pluralizer

It'll treat wrongly 1 and -1 in the same way.
Update pluralization.spec.js
Update CHANGELOG.md
Merge pull request #268 from Sija/patch-1

Don't absolutize count before passing it to pluralizer
! Fix default pluralization for -1
+ Add class FallbackLocales
+ Add spec & code for merging fallbacks
* Set default value to true
~ Modify CHANGELOG and README for the new feature
[ci skip]