[#179] Rename resolver package to ns

`resolver` isn't suitable name for the package with NeoFS name system
functionality.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

README.md

@@ -25,7 +25,7 @@ version prefix and checksum in addition to script-hash.
 ### token
 Contains Bearer token type with several NeoFS-specific methods.
 
-### resolver
+### ns
 In NeoFS there are 2 types of name resolution: DNS and NNS. NNS stands for Neo Name Service
 is just a [contract](https://github.com/nspcc-dev/neofs-contract/) deployed on a Neo blockchain.
 Basically, NNS is just a DNS-on-chain which can be used for resolving container nice-names as well

ns/dns.go

@@ -1,4 +1,4 @@
-package resolver
+package ns
 
 import (
 	"net"

ns/doc.go

@@ -1,5 +1,5 @@
 /*
-Package resolver provides functionality of NeoFS name system.
+Package ns provides functionality of NeoFS name system.
 
 DNS type is designed to resolve NeoFS-related names using Domain Name System:
 	const containerName = "some-container"
@@ -19,4 +19,4 @@ NNS type is designed to resolve NeoFS-related names using Neo Name Service:
 	// ...
 
 */
-package resolver
+package ns

ns/nns.go

@@ -1,4 +1,4 @@
-package resolver
+package ns
 
 import (
 	"context"

ns/nns_test.go

@@ -1,4 +1,4 @@
-package resolver
+package ns
 
 import (
 	"errors"

ns/util.go

@@ -1,4 +1,4 @@
-package resolver
+package ns
 
 import "errors"