Allow spaces or special chars in variables

[raulsh]

Hi,

We are replacing handlebarsrb with this gem, because we need to build our app in ARM. But we are experiencing some issues, for example:

We can't call variables with "spaces". In handlebars we can call variables with [], so inside brackets we can put spaces or other chars:
{{a.b.[DDO.].1.name}}
But in ruby-handlebars this case is not supported
Parslet::ParseFailed (Extra input after last repetition at line 21 char 29.)