This commit gets rid of multiple redundant copies of MarhsalJSON()
method present for all existing IQR. It does so by introducing a
new struct called InlineQueryResultBase, which takes care of new
Type (for JSON) and existing duplicated ID field.
InlineQueryResults is a new helper wrapper for []IQR slices. It
implements MarshalJSON, which makes sure IQR.ID and IQR.Type are
set properly (by computing a hash and infering IQR type).
These changes make it possible to set custom options when responding to
inline queries, as described on
https://core.telegram.org/bots/api#answerinlinequery.
It also includes all the (non-cached) inline result types as described
at https://core.telegram.org/bots/api#inlinequeryresult.
Some remarks:
* The internals of sendCommand have changed. It now expects a
JSON-serializable object. Instead of doing GET requests with
URL-encoded query parameters it now POSTS JSON directly.
* Because of the above, sendFile() has changed as well. It now expects a
* `map[string]string` which it will internally convert to URL encoded
form values.
* Respond has been deprecated in favor of the new AnswerInlineQuery
function. It is only kept for backward compatibility.
* A dependency on https://github.com/mitchellh/hashstructure has been
introduced in order to generate automatic IDs for inline results.
