Transition from `ioutil.ReadFile` to `os.ReadFile`

[emp-temp]

Issue Number

#64

Hello,Mattn.

In response to the issue regarding the deprecation of ioutil.ReadFile in Go 1.16 and the recommendation to use os.ReadFile, this PR addresses that concern.

Changes:

Replaced all instances of ioutil.ReadFile with os.ReadFile throughout the codebase. Adjusted any related code segments to ensure compatibility with the os package's function signature and behavior.

Additional Notes:

The project's Go version has also been updated to 1.16 to align with this change and take advantage of the improvements provided in this version. I've tested the changes extensively, and the transition appears seamless. Still, a thorough review would be highly appreciated to ensure nothing is overlooked.

Thank you for your attention to this matter, and I look forward to your feedback.

Best regards.