Provide read access into lexer settings

[eclarkso]

In some circumstances it might be useful for Environment to provide getters to the lexer_config, e.g.,

const std::string & Environment::get_statement_open() const
{
   return lexer_config.statement_open;
}
// etc

For the time being, I have forked inja and made all members protected so that I can subclass Environment in my own code, but it would be nice to not have to maintain that fork... unless I'm missing another way of effecting the same goal (aside from storing the settings alongside the environment, which seems duplicative and rickety).

If I'm not wrong about that, could either:

• the *_config objects be made protected so subclasses could access them and provide their own getters?
• *_config field getters be added to Environment?

ETA: my realization I forked inja some time ago to change the member visibility