Improved error handling

[nordtechtiger]

Quickbuild currently throws a segfault and coredumps when faced with most incorrect configuration files. This needs to be revamped.

A good starting place would be to tag tokens (and AST fields) with the location of the original data from the config and add a separate error handler which can backtrack and exit gracefully upon an error.

[nordtechtiger]

Note to self: Look into why objects as "foo" yields the correct error origin towards the top of the config file but not the bottom.

[nordtechtiger]

Fixed in 6c35202. I just want to make some more common errors recoverable in builder.cpp, e.g. misspelled variable names, etc.

[nordtechtiger]

9dff725 is ok for now.