Include git hash in bat -V and bat --version output if present

I had to use a `lazy_static` due to that the clap API that only accepts a
reference to a version string. And, in our code, only a 'static reference to a
version string.

Code could probably be refactored to accept a "normal" reference, but that would
be a major undertaking.

CHANGELOG.md

@@ -20,6 +20,7 @@
 
 - Add PowerShell completion, see #1826 (@rashil2000)
 - Minimum supported Rust version (MSRV) bumped to 1.46
+- Include git hash in `bat -V` and `bat --version` output if present. See #1921 (@Enselic)
 
 ## Syntaxes