AST のノードの付け替えを実装

[abap34]

fix #143

ノードの付け替えと必要な AST操作のインターフェースを実装した。

この PR で脚注の実装に必要な全ての機能が実装完了　🎉

import almo


def pretty_print(ast, indent=0, last=False):
    print("  " * indent + f"{'└──' if last else '├──'} {ast}")
    for i, child in enumerate(ast.childs):
        pretty_print(child, indent + 1, i == len(ast.childs) - 1)


md = """
# Footnote Example

**On my way to the store**[^1], I saw a duck.

[^1]: Oatmeal is better than cereal.

Quack.

"""

ast = almo.parse(md)

print("=== AST ===")


pretty_print(ast)


footnote_defs = ast.nodes_byclass("FootnoteDefinition")


print("=== Move Footnote to the end ===")

ast.pushback_child(
    almo.DivBlock("footnote"),
)

ast.move_node(
    footnote_defs[0],
    ast.childs[-1],
)

pretty_print(ast)

=== AST ===
├── <almo.Markdown (uuid: 0)>
  ├── <almo.NewLine (uuid: 1)>
  ├── <almo.Header (uuid: 2)>
    └── <almo.RawText (uuid: 3)>
  ├── <almo.NewLine (uuid: 4)>
  ├── <almo.InlineStrong (uuid: 5)>
    └── <almo.RawText (uuid: 6)>
  ├── <almo.InlineFootnoteReference (uuid: 7)>
  ├── <almo.RawText (uuid: 8)>
  ├── <almo.NewLine (uuid: 9)>
  ├── <almo.FootnoteDefinition (uuid: 10)>
    └── <almo.RawText (uuid: 11)>
  ├── <almo.NewLine (uuid: 12)>
  ├── <almo.RawText (uuid: 13)>
  ├── <almo.NewLine (uuid: 14)>
  └── <almo.NewLine (uuid: 15)>

=== Move Footnote to the end ===
├── <almo.Markdown (uuid: 0)>
  ├── <almo.NewLine (uuid: 1)>
  ├── <almo.Header (uuid: 2)>
    └── <almo.RawText (uuid: 3)>
  ├── <almo.NewLine (uuid: 4)>
  ├── <almo.InlineStrong (uuid: 5)>
    └── <almo.RawText (uuid: 6)>
  ├── <almo.InlineFootnoteReference (uuid: 7)>
  ├── <almo.RawText (uuid: 8)>
  ├── <almo.NewLine (uuid: 9)>
  ├── <almo.NewLine (uuid: 12)>
  ├── <almo.RawText (uuid: 13)>
  ├── <almo.NewLine (uuid: 14)>
  ├── <almo.NewLine (uuid: 15)>
  └── <almo.DivBlock (uuid: 16)>
    └── <almo.FootnoteDefinition (uuid: 10)>
      └── <almo.RawText (uuid: 11)>