add support for git-lfs to support archives (#16)

This greatly speeds up the usage of generated index repositories as
these are only extracted, not build with tons of git invocations.

Author: Byron

.gitattributes

@@ -0,0 +1,5 @@
+**/generated-archives/*.tar.xz filter=lfs diff=lfs merge=lfs -text
+
+# assure line feeds don't interfere with our working copy hash 
+**/tests/fixtures/*.sh text crlf=input	eol=lf
+

.github/workflows/rust.yml renamed to .github/workflows/ci.yml

@@ -11,6 +11,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
+    - uses: Swatinem/rust-cache@v2
+    - run: git lfs fetch && git lfs checkout
     - name: tests
       run: make test
     - name: docs