Add support for the SegTree and LazySegTree with open ended ranges

[ngng628]

• Tests pass
• Appropriate changes to README are included in PR

Overview

• 標準ライブラリに合わせて Range で open ended ranges に対応させました。
  • tree[..3]
  • tree[1..]
  • tree[...]

[codecov-commenter]

Codecov Report

Merging #24 (3a9f365) into master (2832b71) will increase coverage by 0.27%.
The diff coverage is 100.00%.

❗ Current head 3a9f365 differs from pull request most recent head a95ccb8. Consider uploading reports for the commit a95ccb8 to get more accurate results

@@            Coverage Diff             @@
##           master      #24      +/-   ##
==========================================
+ Coverage   81.95%   82.23%   +0.27%     
==========================================
  Files          14       14              
  Lines        1092     1092              
==========================================
+ Hits          895      898       +3     
+ Misses        197      194       -3     

Files Changed	Coverage Δ
src/lazy_seg_tree.cr	85.61% <100.00%> (+1.43%)	⬆️
src/seg_tree.cr	82.35% <100.00%> (+1.17%)	⬆️

[hakatashi]

変更内容は良さそうです!

• ユニットテストを追加してください
• masterのほうをいじったのでrebaseかmergeをお願いします

[ngng628]

変更内容は良さそうです!

• ユニットテストを追加してください
• masterのほうをいじったのでrebaseかmergeをお願いします

追加しました！

[hakatashi]

ありがとうございます!