v0: Configuration support

[ingydotnet]

The YS compiler and runtime need to be configurable.

There are 2 main ways that YS code is compiled and evaluated and each need configuration:

1. The ys (ys-0) CLI command.
   Needs to take a --config=<config-file> option (or YS_CONFIG var or default config file like ~/.yamlscript/config.yaml).
2. A programming language libyamlscript.so binding library has a YAMLScript::Loader class that will need to be instantiated with a YAMLScript::Config class.

The required configuration keys are yet to be determined but they need to default to no code evaluation.