Add encoding to utfbom reader structure

[peczenyj]

Hello

I note that we may lost the original encoding if we wrap the *utfbom.Reader again.

This will ensure that we will return the original encoding instead Unknown

Also, I made some modifications to code and tests to ensure better readability. for instance, now all tests are running in parallel, all tests may have subtests, we stop use deprecated libraries such as io/ioutil, etc.

I also add one basic Makefile to help run tests, etc.

And drop support/ tests for old versions of go -- we are in the 1.21.1 right now

Regards

[peczenyj]

Fixes #10 , #11 and #12

[dimchansky]

Hi @peczenyj,

First off, thank you so much for your contribution to the project! I've reviewed the pull request and have merged it. However, I noticed that the Makefile uses utilities like golint, gofumpt, and goimports. While these are essential tools, they might not be present on every developer's machine.

To streamline our development process, I suggest we add an additional step in the Makefile for installing these necessary utilities. This step will ensure that the right versions of the utilities are installed, making our setup more robust and developer-friendly.

Additionally, I agree that having a Makefile is beneficial for the project. Considering the transition from Travis CI to GitHub Actions, the Makefile will play a crucial role in simplifying and automating our build process. This move aligns well with our goals for a more efficient and modern development workflow.

Looking forward to your thoughts on this, and thanks again for your valuable contribution!