Add good bit of functionality, some tests

Signed-off-by: Vartan Benohanian <vartanbeno@gmail.com>

vote.go

@@ -0,0 +1,67 @@
+package geddit
+
+import (
+	"context"
+	"fmt"
+	"net/url"
+)
+
+// VoteService handles communication with the upvote/downvote
+// related methods of the Reddit API
+type VoteService interface {
+	Up(ctx context.Context, id string) (*Response, error)
+	Down(ctx context.Context, id string) (*Response, error)
+	Remove(ctx context.Context, id string) (*Response, error)
+}
+
+// VoteServiceOp implements the Vote interface
+type VoteServiceOp struct {
+	client *Client
+}
+
+var _ VoteService = &VoteServiceOp{}
+
+type vote int
+
+// Reddit interprets -1, 0, 1 as downvote, no vote, and upvote, respectively.
+const (
+	downvote vote = iota - 1
+	novote
+	upvote
+)
+
+func (s *VoteServiceOp) vote(ctx context.Context, id string, vote vote) (*Response, error) {
+	path := "api/vote"
+
+	form := url.Values{}
+	form.Set("id", id)
+	form.Set("dir", fmt.Sprint(vote))
+	form.Set("rank", "10")
+
+	req, err := s.client.NewPostForm(path, form)
+	if err != nil {
+		return nil, err
+	}
+
+	resp, err := s.client.Do(ctx, req, nil)
+	if err != nil {
+		return resp, err
+	}
+
+	return resp, nil
+}
+
+// Up upvotes a link or a comment
+func (s *VoteServiceOp) Up(ctx context.Context, id string) (*Response, error) {
+	return s.vote(ctx, id, upvote)
+}
+
+// Down downvotes a link or a comment
+func (s *VoteServiceOp) Down(ctx context.Context, id string) (*Response, error) {
+	return s.vote(ctx, id, downvote)
+}
+
+// Remove removes the user's vote on a link or a comment
+func (s *VoteServiceOp) Remove(ctx context.Context, id string) (*Response, error) {
+	return s.vote(ctx, id, novote)
+}