We now no longer call malloc/free/... directly, but use an allocator object
that is passed around.
This was mainly done as a preparation for a garbage collector: The
collector will need to know, how much memory we're using, introducing the
collector abstraction will allow the GC to hook into the memory allocation
and observe the memory usage.
This has other potential applications:
- We could now be embedded into applications that can't use the libc
allocator.
- There could be an allocator that limits the total amount of used memory,
e.g. for sandboxing purposes.
- In our tests we could use this to simulate out of memory conditions
(implement an allocator that fails at the n-th allocation, increase n by
one and restart the test until there are no more faked OOM conditions).
The function signature of the allocator is basically exactly the same as
the one Lua uses.
This avoids creating refcounted strings during evaluation and makes it
easier to use the same parsed string in multiple places (should be
useful once we implement functions).
If you assign into a member access (`foo.bar = baz` or `foo@bar = baz`), it
is no longer permitted that the LHS of the at/dot is an arbitrary
assignable. It now must be a variable, at or dot. This disallows some silly
constructs (e.g. `[foo]@bar = baz`), increases the similarity to function
parameters and should make writing the evaluation code for these more easy.
The previous representation didn't properly model the fact that an
assignable / parameter can only be expanded, if it's a list element. This
now better models this. Other than being more correct, this should also
make evaluating these a bit easier.
While I was at it, I also improved the error message for multiple
expansions on the same level and added tests for these.
