Possibility for taglib static builds

[xbt573]

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

1. Building go-sqlite3 statically is very easy, just pass -ldflags '-linkmode external -extldflags "-static"' to go build

2. 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]

thanks! ill try this