Add apidocs to #tap and #dup

[hachi8833]

Added the api documents to #tap and #dup.

Ref: #788 and #791

I hope my understanding is correct, especially on Hash#dup.

[codecov]

Codecov Report

Merging #792 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #792   +/-   ##
=======================================
  Coverage   80.31%   80.31%           
=======================================
  Files          54       54           
  Lines        7431     7431           
=======================================
  Hits         5968     5968           
  Misses       1236     1236           
  Partials      227      227

Impacted Files	Coverage Δ
vm/array.go	96.17% <ø> (ø)	⬆️
vm/class.go	85.8% <ø> (ø)	⬆️
vm/hash.go	96.81% <ø> (ø)	⬆️
vm/string.go	98.27% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a97e245...357d650. Read the comment docs.

[st0012]

@hachi8833 sorry that I should warn you about object_id doesn't actually function like Ruby. Even if you call it on the same object it returns different numbers every time.
I will try to fix this issue first. It that works out well, we can merge this PR after the fix. If that didn't work, you'll need to use different examples in your doc 😞

[hachi8833]

Thank you for the explanation! I'll try it after the fix.

[st0012]

@hachi8833 the issue of object_id has been fixed and merged, feel free to reopen this PR!