Leading and trailing whitespaces get stripped in text grammar

[MarcCote]

At the moment, when parsing the grammar files, whitespaces found at the start or the end of expansions are getting stripped. This might also been the case with the old way of loading grammar files.

To reproduce the issue:
tw-make custom --quest-breadth 3 --quest-length 3 --seed 24853 --output tw_games/test.ulx
tw-play ./tw_games/test.ulx

Welcome to TextWorld! Here is your task for today. First, it would be good if
you could make an effort to head east.After that,recover the key from the
kitchen. And if you do that, you're the winner!

Note the whitespaces in house_instructions.twg

...
emptyinstruction1: And then, ;
emptyinstruction2: Then, ;
emptyinstruction3: After that, ;
emptyinstruction4: And then, ;
emptyinstruction5: After that, ;
emptyinstruction6: Then, ;
emptyinstruction7: And then, ;
emptyinstruction8: After that, ;
emptyinstruction9: And then, ;
emptyinstruction10: Then, ;

[MarcCote]

This seems fixed now.