git: add q script

"Q" stands for "query": Inspired by MJD [1], add my own version. Mine
shows symbolic refs like the input by default, but expands to short
hashes with `-v`. It also collapses equivalent refs (because `show`
does) instead of running a command for each input (which is expensive).

Here's hyperfine output:

    hyperfine --output=pipe 'git q2 HEAD origin/master~{1..1000}' 'git q HEAD origin/master~{1..1000}'
    Benchmark 1: git q2 HEAD origin/master~{1..1000}
      Time (mean ± σ):      9.524 s ±  0.012 s    [User: 4.540 s, System: 3.397 s]
      Range (min … max):    9.510 s …  9.547 s    10 runs

    Benchmark 2: git q HEAD origin/master~{1..1000}
      Time (mean ± σ):     163.7 ms ±   1.9 ms    [User: 99.8 ms, System: 54.8 ms]
      Range (min … max):   160.8 ms … 168.2 ms    17 runs

    Summary
      git q HEAD origin/master~{1..1000} ran
       58.18 ± 0.70 times faster than git q2 HEAD origin/master~{1..1000}

The 2 commands produce identical output (although q2 used different
lengths with -v sometimes), where q2 is the same as q with this patch:

    38c38
    < exec git show -s --format="$id $query" "$@"
    ---
    > for ref; do git show -s --format="$id $query" "$ref"; done

[1]: https://blog.plover.com/prog/git-q.html

links/bin/git-q

@@ -0,0 +1,38 @@
+#! /bin/sh
+
+# Inspired by: https://github.com/mjdominus/git-util/blob/master/bin/git-q
+
+set -eu
+
+OPTIONS_SPEC="\
+$(basename -- "$0" | sed -e 's/-/ /') [-v] <spec-or-ref> [<ref>…]
+
+Query refs for data using pretty-format specs (default: %cd)
+--
+v verbose: show commit IDs instead of input refs"
+SUBDIRECTORY_OK=true
+
+# source git-sh-setup for some helpers
+set +u
+. "$(git --exec-path)"/git-sh-setup
+set -u
+
+id=%S
+
+while test $# -gt 0; do
+  opt="$1"
+  shift
+  case "$opt" in
+    (-v) id=%h ;;
+    (--) break ;;
+  esac
+done
+test $# -eq 0 && usage
+
+query=%cd
+case "$1" in
+  (%*) query="$1"; shift ;;
+esac
+test $# -eq 0 && usage
+
+exec git show -s --format="$id $query" "$@"