libtree 0.1.0

a crate for general or game tree
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# libtree : a crate for game tree

gtree is a crate that implements trees in Rust, taking huge inspirations from [Rust with too
many linked lists](https://rust-unofficial.github.io/too-many-lists/) (so it is as useless and
stupid as
it's inspiration). The main purpose of this crate was to implements tree for game tree needed
in a crate for game theory.

# Nomenclature
Just a bit of nomemclature to be make my documentation slighty more readable.
- a node is a set of pointers (one for the father and another collection for the childs) and
also stores an element, often abbreviated into elem or el.
- a tree is composed of two pointers towards nodes :
    - 'current', where you are in the tree.
    - 'root', explicit.
- the subtree will designates the tree that is rooted at 'current' in a tree.
- a cursor is another pointer to a node of the tree, but without a root associated.

# Showcase
## Creation and adding elements
gtree provides the [Tree] structure to create a store a tree, and add new element to it.
```rust
use gtree::Tree;
let mut tree = Tree::from_element(1);
tree.push(2);
```

## Navigation
By navigation, we mean moving around 'current' in the tree. But as the term move has already a
signication in Rust, we use the term navigation in this crate.
Tree supports three type of navigation :
- `navigate_to(idx)` which navigates 'current' to its `idx` child (if possible).
- `ascend()` which navigates 'current' to its father (if possible i.e. not at 'root').
- `go_to_root()` which navigates 'current' to 'root'.
```rust
assert_eq!(tree.peek(), &1);
tree.navigate_to(0);
assert_eq!(tree.peek(), &2);
tree.push(3);
tree.ascend();
assert_eq!(tree.into_vec(), vec![1, 2, 3]);
```

## Joining and splitting
`Tree`s can be joined and splitted. Splitting tree is for the moment the best way to drop
unwantted part of the tree.
```rust
let mut tree1 = Tree::from_element(1);
tree1.push_iter(vec![2, 3]);
let mut tree2 = Tree::from_element(4);
tree2.push_iter(vec![5, 6]);
tree1.join(tree2, 0);
// exploration is always made in depth first way
assert_eq!(tree1.iter().collect::<Vec<&i32>>(), vec![&1, &4, &5, &6, &2, &3]);
let mut tree2 = tree1.split(0);
assert_eq!(tree2.into_vec(), vec![4, 5, 6]);
```

## Cursors
Cursors are of three differents types and allows concurrent exploration of the tree.
```rust
let mut cursor1 = tree1.cursor();
let cursor2 = tree1.cursor();
cursor1.navigate_to(1);
assert_eq!(cursor1.peek(), &3);
assert_eq!(cursor2.peek(), &1);
```

## Subtrees
Most exploration methods when called will only explore the subtree rooted as 'current' (for a
tree or a cursor).
```rust
let mut tree = Tree::from_element(1);
tree.push_iter(vec![4, 2, 1]);
tree.navigate_to(0);
tree.push_iter(vec![5, 6]);
assert_eq!(tree.iter().collect::<Vec<&i32>>(), vec![&4, &5, &6]);
let mut cursor = tree.cursor_mut();
cursor.ascend();
cursor.navigate_to(1);
cursor.push(10);
assert_eq!(cursor.iter_mut().collect::<Vec<&mut i32>>(), vec![&mut 2, &mut 10]);
```