build: change the fallback version suffix to `+git.{sha}`

Seems to be more commonly used than the current `-commit-{sha}`.
Also cleanup/simplify the version handling code.

Change-Id: I551c78632037c7156319b7ff7a327980f73ce265
diff --git a/README.md b/README.md
index 54a66c5..eee22fe 100644
--- a/README.md
+++ b/README.md
@@ -1,9 +1,9 @@
 # NDN Essential Tools
 
+![Latest version](https://img.shields.io/github/v/tag/named-data/ndn-tools?label=Latest%20version)
+![Language](https://img.shields.io/badge/C%2B%2B-17-blue)
 [![CI](https://github.com/named-data/ndn-tools/actions/workflows/ci.yml/badge.svg)](https://github.com/named-data/ndn-tools/actions/workflows/ci.yml)
 [![Docs](https://github.com/named-data/ndn-tools/actions/workflows/docs.yml/badge.svg)](https://github.com/named-data/ndn-tools/actions/workflows/docs.yml)
-![Language](https://img.shields.io/badge/C%2B%2B-17-blue)
-![Latest version](https://img.shields.io/github/v/tag/named-data/ndn-tools?label=Latest%20version)
 
 This repository contains a collection of basic tools for [Named Data Networking (NDN)](https://named-data.net/).
 The tools currently included are: