Update goleveldb dependency

vendor/github.com/syndtr/goleveldb/README.md

@@ -0,0 +1,105 @@
+This is an implementation of the [LevelDB key/value database](http:code.google.com/p/leveldb) in the [Go programming language](http:golang.org).
+
+[![Build Status](https://travis-ci.org/syndtr/goleveldb.png?branch=master)](https://travis-ci.org/syndtr/goleveldb)
+
+Installation
+-----------
+
+	go get github.com/syndtr/goleveldb/leveldb
+
+Requirements
+-----------
+
+* Need at least `go1.4` or newer.
+
+Usage
+-----------
+
+Create or open a database:
+```go
+db, err := leveldb.OpenFile("path/to/db", nil)
+...
+defer db.Close()
+...
+```
+Read or modify the database content:
+```go
+// Remember that the contents of the returned slice should not be modified.
+data, err := db.Get([]byte("key"), nil)
+...
+err = db.Put([]byte("key"), []byte("value"), nil)
+...
+err = db.Delete([]byte("key"), nil)
+...
+```
+
+Iterate over database content:
+```go
+iter := db.NewIterator(nil, nil)
+for iter.Next() {
+	// Remember that the contents of the returned slice should not be modified, and
+	// only valid until the next call to Next.
+	key := iter.Key()
+	value := iter.Value()
+	...
+}
+iter.Release()
+err = iter.Error()
+...
+```
+Seek-then-Iterate:
+```go
+iter := db.NewIterator(nil, nil)
+for ok := iter.Seek(key); ok; ok = iter.Next() {
+	// Use key/value.
+	...
+}
+iter.Release()
+err = iter.Error()
+...
+```
+Iterate over subset of database content:
+```go
+iter := db.NewIterator(&util.Range{Start: []byte("foo"), Limit: []byte("xoo")}, nil)
+for iter.Next() {
+	// Use key/value.
+	...
+}
+iter.Release()
+err = iter.Error()
+...
+```
+Iterate over subset of database content with a particular prefix:
+```go
+iter := db.NewIterator(util.BytesPrefix([]byte("foo-")), nil)
+for iter.Next() {
+	// Use key/value.
+	...
+}
+iter.Release()
+err = iter.Error()
+...
+```
+Batch writes:
+```go
+batch := new(leveldb.Batch)
+batch.Put([]byte("foo"), []byte("value"))
+batch.Put([]byte("bar"), []byte("another value"))
+batch.Delete([]byte("baz"))
+err = db.Write(batch, nil)
+...
+```
+Use bloom filter:
+```go
+o := &opt.Options{
+	Filter: filter.NewBloomFilter(10),
+}
+db, err := leveldb.OpenFile("path/to/db", o)
+...
+defer db.Close()
+...
+```
+Documentation
+-----------
+
+You can read package documentation [here](http:godoc.org/github.com/syndtr/goleveldb).