Inject version with embed instead of build flags

The build flags made the basic build and debug calls quite complex and
bound this strictly to Git repositories which is a problem if the source
code is passed around as tar archive.

Embedding this via Go's embed package and a VERSION.txt file makes this
way easier. A simple `go build` command is sufficient to build ceres.

To make sure the version string is extended by a `-devel` marker and
that this marker is removed before a release a RELEASE.md file was added
as a checklist for releases.

1 files changed, 3 insertions, 1 deletions

diff --git a/version.go b/version.go
index f9a997e..087666e 100644
--- a/version.go
+++ b/version.go
@@ -2,12 +2,14 @@ package main
 
 import (
 	"log"
+	_ "embed"
 )
 
+//go:embed VERSION.txt
 var version string
 
 func init() {
 	if version == "" {
-		log.Fatal("No version information passed to this via build flags")
+		log.Fatal("Bad build: No version string embedded.")
 	}
 }