Allow for the exclusion of files from backups (#100)

* Hoist walking of files so it can be used for features other than archive creation

* Add option to ignore files from backup using glob patterns

* Use Regexp instead of glob for exclusion

* Ignore artifacts

* Add teardown to test

* Allow single Re for filtering only

* Add documentation

* Use MatchString on re, add bad input to message in case of error

test/ignore/run.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+
+set -e
+
+cd $(dirname $0)
+mkdir -p local
+
+docker-compose up -d
+sleep 5
+docker-compose exec backup backup
+
+docker-compose down --volumes
+
+out=$(mktemp -d)
+sudo tar --same-owner -xvf ./local/test.tar.gz -C "$out"
+
+if [ ! -f "$out/backup/data/me.txt" ]; then
+  echo "[TEST:FAIL] Expected file was not found."
+  exit 1
+fi
+echo "[TEST:PASS] Expected file was found."
+
+if [ -f "$out/backup/data/skip.me" ]; then
+  echo "[TEST:FAIL] Ignored file was found."
+  exit 1
+fi
+echo "[TEST:PASS] Ignored file was not found."