Allow specifying commands as an array of arguments

Currently, all commands are accepted as a single string. This requires shell escaping in order to work correctly. We should additionally allow commands to be passed as an array of strings, where the first item is the program name and the remaining items are the arguments.

This should be done in such a way that the parsing returns an error if the command array is empty.

compile = "rustc -o solution solution.rs"

should be equivalent to

compile = ["rustc", "-o", "solution", "solution.rs"]