Create .gitattributes (#269)

This PR adds a .gitattributes file to exclude specific files and directories from exports/installing composer package. 

Purpose:

    Keeps repository metadata and tooling files out of distribution packages.
    Follows best practices for cleaner project exports.

Impact:

No runtime changes—this only affects repository operations like git archive.

Author: KarelWintersky

.gitattributes

@@ -0,0 +1,18 @@
+* text=auto
+* eol=lf
+
+.git                export-ignore
+.gitattributes      export-ignore
+.gitignore          export-ignore
+CREDITS             export-ignore
+phpcs-ruleset.xml   export-ignore
+phpdoc.xml          export-ignore
+phpunit.xml         export-ignore
+scrutinizer.yml     export-ignore
+.github             export-ignore
+examples            export-ignore
+tests               export-ignore
+API-1.0.0           export-ignore
+RELEASE-2.0.0       export-ignore
+CONTRIBUTING.md     export-ignore
+CHANGELOG.md        export-ignore