Readme/golint: improve readme with gx instructions. Make golint happy.

License: MIT
Signed-off-by: Hector Sanjuan <hector@protocol.ai>

set.go

 package cid
 
+// Set is a implementation of a set of Cids, that is, a structure
+// to which holds a single copy of every Cids that is added to it.
 type Set struct {
 	set map[string]struct{}
 }
 
+// NewSet initializes and returns a new Set.
 func NewSet() *Set {
 	return &Set{set: make(map[string]struct{})}
 }
 
+// Add puts a Cid in the Set.
 func (s *Set) Add(c *Cid) {
 	s.set[string(c.Bytes())] = struct{}{}
 }
 
+// Has returns if the Set contains a given Cid.
 func (s *Set) Has(c *Cid) bool {
 	_, ok := s.set[string(c.Bytes())]
 	return ok
 }
 
+// Remove deletes a Cid from the Set.
 func (s *Set) Remove(c *Cid) {
 	delete(s.set, string(c.Bytes()))
 }
 
+// Len returns how many elements the Set has.
 func (s *Set) Len() int {
 	return len(s.set)
 }
 
+// Keys returns the Cids in the set.
 func (s *Set) Keys() []*Cid {
 	out := make([]*Cid, 0, len(s.set))
 	for k := range s.set {
@@ -34,6 +42,8 @@ func (s *Set) Keys() []*Cid {
 	return out
 }
 
+// Visit adds a Cid to the set only if it is
+// not in it already.
 func (s *Set) Visit(c *Cid) bool {
 	if !s.Has(c) {
 		s.Add(c)
@@ -43,6 +53,8 @@ func (s *Set) Visit(c *Cid) bool {
 	return false
 }
 
+// ForEach allows to run a custom function on each
+// Cid in the set.
 func (s *Set) ForEach(f func(c *Cid) error) error {
 	for cs := range s.set {
 		c, _ := Cast([]byte(cs))