Relocate files to remove redundant directories

[uuf6429]

This PR does what was suggested here. I thought it would make sense / be cleaner to make a separate PR.

Changes:

1. ./src is now loaded as PSR-4
2. ./src represents Behat\Gherkin\
3. ./tests represents Tests\Behat\Gherkin\
4. fixed namespace of existing test

⚠️ I've added a git-ignore-blame entry, so this PR should not be squashed when accepted.

[acoulton]

@uuf6429 I rebased and force pushed this to resolve the conflict with #282 (as that PR still had the previous proposal for changing the composer.json autoload config).

The commits are still showing as yours but now showing a warning that they're unverified (as I obviously can't sign as you). Feel free to rebase and force push again to resolve that.

I have dropped the commit with the git-blame-ignore (the commit ref was outdated anyway) - AFAIK this is not actually required/appropriate for straight file moves, if you look at the blame on https://github.com/uuf6429/Gherkin/blame/chore/relocate-files/tests/ParserTest.php you'll see that it is correctly showing the history despite the file move.

I don't think that conflicts with other PRs will be an issue - the majority are old and have conflicts already anyway, and I've generally found git is usually quite reliable about resolving file renames so it should be quick enough to update anything that needs it.

[uuf6429]

@acoulton done, thanks for taking the time to fix things.

[acoulton]

Great, thanks :-)