Support consul's watch feature

[dysinger]

When you watch something on Consul, it's a blocking HTTP request. Right now I'm passing in a managersettings to initializeConsulClient that disables the timeout when I want to watch things. This means I have to use two different consul clients & juggle them (because I don't want the no-timeout client used for non-watch requests.) Ideally I would manage my own manager & I could modify the request to never timeout if I wanted to watch data for changes on that one HTTP request.

Related to #2

Both #2 and #3 are blocking issue #1 IMHO

[sseveran]

@dysinger is this something you are interested in working on? I don't use watches currently and am unlikely to have time to implement them in the near term.

[dysinger]

@sseveran I think this is solved by #4 (the only difference with watch is that you getKey with an index without timing out the HTTP request).

[sseveran]

I think the larger issue is what is the best way to design the API on the haskell side. Any query can be made blocking but setting its timeout to Nothing. As I understand it the handler is a script/executable that can be called by the consul agent for each event. It might be possible to use rpc of some sort to get those messages back into an applications. What are your thoughts?