Grow-only N-ary tree storing elements of type E.
TODO: Complete. TODO: Default Allocator to a suitable default growth-only allocator.
https://en.wikipedia.org/wiki/M-ary_tree
http://forum.dlang.org/post/prsxfcmkngfwomygmthi@forum.dlang.org
See Implementation
Grow-only N-ary tree storing elements of type E.
TODO: Complete. TODO: Default Allocator to a suitable default growth-only allocator.