Minor improvements to the setup

[junedev]

I had a look at the current state and noticed a couple of minor things we might want to address:

• Currently there is no test case that covers the multiple files case
• Is there any reason we call the file with the test fixtures tests and not testdata which is the official name?
• Would be good to have a .gitignore file that contains vendor in case someone runs in vendored mode, the represent executable that is created when running the command from the readme and any .exe files that are created on Windows
• Would be good if the readme also showed an example command that would actually run, I found this very helpful with the testrunner, e.g. ./represent hamming ./representer/tests/hamming/1 . (not sure how it looks for windows)

cc @tehsphinx

[junedev]

I also noticed there is no CI (GitHub Action) yet to run the unit tests.

[tehsphinx]

Left to do: CI

• unit tests
• linters