Refactored the handling of the stashToken to avoid using a stack
Refactored the handling of the stashToken to avoid using a stack

Given that we only need to stash 1 token at a time now, using a stack is
not necessary. And this avoids reaching the broken code of PHP 5.6-beta1
and 5.6-beta2.
Closes #77

higrow/Gherkin,stof/Gherkin,Behat/Gherkin,dav-m85/Gherkin,unkind/Gherkin