Possibility for taglib static builds

gonic version: v0.16.4 docker tag: latest Actually this is irrelevant to issue, but nevermind.

Building go-sqlite3 statically is very easy, just pass -ldflags '-linkmode external -extldflags "-static"' to go build
taglib requires static rebuild and some code changes, but nothing very hard Firstly we need to build taglib as static library: pass -DBUILD_SHARED_LIBS=OFF to cmake (this is confusing, but disabling shared libraries enables static :/) Static zlib is also needed, which is not always bundled with system package (on alpine use zlib-static) Needed code change is at https://github.com/sentriz/audiotags/blob/master/audiotags.go#L25: add zlib to pkg-config
```
--- a/audiotags.go
+++ b/audiotags.go
@@ -22,7 +22,7 @@
package audiotags

/*
-#cgo pkg-config: taglib
+#cgo pkg-config: taglib zlib
#cgo LDFLAGS: -lstdc++
#include "audiotags.h"
#include <stdlib.h>
```

Final build command is:

go build -ldflags '-linkmode external -extldflags "-static"' -o gonic cmd/gonic/gonic.go

ldd shows:

/lib/ld-musl-x86_64.so.1: gonic: Not a valid dynamic program

(whole process was made in alpine docker image)

I didn't send PR because this is mostly untested (at least i could build it statically)

sentriz / gonic