refactor: Unify error return code

[splasky]

These commits fixed the following things: Renmae http_retcode_t to retcode_t for general error and status coverage. Add new status code inside utils/defined_error.h if you needed.

closes #37

[jserv]

The changes did not reflect the subject of this pull request.

[jserv]

Don't mix copyright date change and return type tweaks in single pull request.

[jserv]

You have to explain why and how you would like to perform these changes within both pull request and commit messages.

[howjmay]

@jserv This PR was originally open by me. I aimed to use a unique error return code throughout TA-endpoint

[jserv]

@jserv This PR was originally open by me. I aimed to use a unique error return code throughout TA-endpoint

Make the task great again. Improve the descriptions in both issue tracker and pull request.

[howjmay]

@jserv This PR was originally open by me. I aimed to use a unique error return code throughout TA-endpoint

Make the task great again. Improve the descriptions in both issue tracker and pull request.

I will open a issue tracker for these.

[jserv]

Use git rebase -i to rework commit messages. Less commits and more expressions.

[jserv]

Always say, "Tangle-accelerator." Be aware of the formal term.

[jserv]

There were some grammar errors in git commit messages. Use shell checkers to validate.

[jserv]

"Fix memory leak" should take place in another pull request.

[jserv]

Issue #37 explained the motivation and considerations for this change, and the commit message of this pull request and git should extend it as well.

[jserv]

The message

Renmae http_retcode_t to retcode_t for general error coverage. lacks of informative reasons.