Add a startup configuration file for flowr

[Ellpeck]

Configuration files should be parsed from the current working directory or parent directories (?) as well as next to the executable (?)

Options we want to support:

• allow disabling source parsing and analyzing (Feat: Follow up on source calls #605)

[Ellpeck]

@EagleoutIce Would you mind specifying some more info about what you think the configuration file should be, specifically

• paths that get checked: should we do the "move upwards through parent directories indefinitely and find all config files there" thing? should we check the executable directory in addition to the working directory?
• config parsing: should checking multiple files cause entries to be overridden/merged? If so, in what direction?
• config format: should the config file be json? or yaml? or something else?

[EagleoutIce]

I would say:

• move upwards the dir chain until a configuration is found
• we only use the "closest" definition (maybe, later, we can talk about global defaults etc.)
• i think a json is easiest to implement