Add configuration for git

- Add .config/git/config
  + Define aliases
  + Configure default behavior in various situations
  + Add user information with signing key
- Add .config/git/commit_msg_template.txt
- Add .config/git/ignore
- Integrate `git` aliases into the shell

.local/bin/git-match-remote

@@ -0,0 +1,35 @@
+#!/bin/sh
+
+# Make all local branches match the remote branch they track,
+# discarding local-only commits and, on the current branch,
+# uncommitted changes as well
+#
+# Branches without an upstream are left alone
+#
+# Usage: git match-remote
+
+set -eu
+
+
+git fetch --all --prune
+
+
+current="$(git branch --show-current)"
+
+
+git for-each-ref --format='%(refname:short) %(upstream:short)' refs/heads/ |
+while read -r branch upstream; do
+
+    [ -n "$upstream" ] || continue
+
+    git rev-parse --verify --quiet "$upstream" >/dev/null || continue
+
+    if [ "$branch" = "$current" ]; then
+        git reset --hard "$upstream"
+        continue
+    fi
+
+    git branch -f "$branch" "$upstream"
+    echo "Moved $branch to $upstream"
+
+done