Adds support for context.Context

[alindeman]

The context package is the most official way to timeout or otherwise cancel requests in Go >= 1.7.

For some prior art from other open source clients, see go-github and go-asana.

Example of generated code:

// Get sends a GET request and decodes the response into v.
func (s *Service) Get(ctx context.Context, v interface{}, path string, query interface{}, lr *ListRange) error {
        return s.Do(ctx, v, "GET", path, nil, query, lr)
}


// Info for account.
func (s *Service) AccountInfo(ctx context.Context) (*AccountInfoResult, error) {
        var account AccountInfoResult
        return &account, s.Get(ctx, &account, fmt.Sprintf("/account"), nil, nil)
}

[cyberdelia]

Looks fine 👍