Add signing and verification to the signature package

vendor/github.com/mtrmac/gpgme/callbacks.go

@@ -0,0 +1,42 @@
+package gpgme
+
+import (
+	"sync"
+)
+
+var callbacks struct {
+	sync.Mutex
+	m map[int]interface{}
+	c int
+}
+
+func callbackAdd(v interface{}) int {
+	callbacks.Lock()
+	defer callbacks.Unlock()
+	if callbacks.m == nil {
+		callbacks.m = make(map[int]interface{})
+	}
+	callbacks.c++
+	ret := callbacks.c
+	callbacks.m[ret] = v
+	return ret
+}
+
+func callbackLookup(c int) interface{} {
+	callbacks.Lock()
+	defer callbacks.Unlock()
+	ret := callbacks.m[c]
+	if ret == nil {
+		panic("callback pointer not found")
+	}
+	return ret
+}
+
+func callbackDelete(c int) {
+	callbacks.Lock()
+	defer callbacks.Unlock()
+	if callbacks.m[c] == nil {
+		panic("callback pointer not found")
+	}
+	delete(callbacks.m, c)
+}