Decouple version into its own package

This allows us to import the package and use version
elsewhere throughout the codebase and set the right version
during the release via build flags.

main.go

@@ -4,13 +4,14 @@ import (
 	"os"
 
 	"github.com/hashicorp/terraform-ls/commands"
+	"github.com/hashicorp/terraform-ls/version"
 	"github.com/mitchellh/cli"
 )
 
 func main() {
 	c := &cli.CLI{
 		Name:    "terraform-ls",
-		Version: "0.1.0",
+		Version: version.String(),
 		Args:    os.Args[1:],
 	}
 

version/version.go

@@ -0,0 +1,36 @@
+package version
+
+import (
+	"fmt"
+
+	version "github.com/hashicorp/go-version"
+)
+
+// The main version number that is being run at the moment.
+var Version = "0.1.0"
+
+// A pre-release marker for the version. If this is "" (empty string)
+// then it means that it is a final release. Otherwise, this is a pre-release
+// such as "dev" (in development), "beta", "rc1", etc.
+var Prerelease = "dev"
+
+// SemVer is an instance of version.Version. This has the secondary
+// benefit of verifying during tests and init time that our version is a
+// proper semantic version, which should always be the case.
+var SemVer *version.Version
+
+func init() {
+	SemVer = version.Must(version.NewVersion(Version))
+}
+
+// ServerName is the name used to send to clients as a way
+// to identify itself in the LSP
+const ServerName = "hashicorp/terraform-ls"
+
+// String returns the complete version string, including prerelease
+func String() string {
+	if Prerelease != "" {
+		return fmt.Sprintf("%s-%s", Version, Prerelease)
+	}
+	return Version
+}