Provide Method to update the URL in a RequestBuilderWrapper and maintain modifications to the BoundRequestBuilder

[rabeyta]

See #56 for the background.

I have two commits here per my initial analysis and suggestions in #56 . Based on feedback I can keep them both, remove one, or change the PR to a more optimal solution.

edit - removed the one commit i didn't like after discussion in the issue and updated the doc for the set url method

[codecov-io]

Codecov Report

Merging #57 into master will increase coverage by 0.17%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master      #57      +/-   ##
============================================
+ Coverage      90.2%   90.38%   +0.17%     
- Complexity     1947     1958      +11     
============================================
  Files           141      141              
  Lines          5790     5804      +14     
  Branches        765      765              
============================================
+ Hits           5223     5246      +23     
+ Misses          387      379       -8     
+ Partials        180      179       -1

Impacted Files	Coverage Δ	Complexity Δ
...e/client/asynchttp/ning/RequestBuilderWrapper.java	100% <100%> (ø)	11 <8> (+8)	⬆️
...ient/asynchttp/netty/StreamingAsyncHttpClient.java	73.42% <0%> (+0.46%)	38% <0%> (+1%)	⬆️
...oste/server/handler/IdleChannelTimeoutHandler.java	92.3% <0%> (+53.84%)	4% <0%> (+2%)	⬆️

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[nicmunroe]

Based on our discussion in issue #56, go ahead and add the getters/setters to RequestBuilderWrapper (option 1) and get rid of the option 2 code. And while you're in there we might as well make everything mutable (HTTP method, circuit breaker stuff). If HTTP method turns out to really truly not be mutable then that's fine, just ignore it.

[rabeyta]

@nicmunroe Sounds good. i've updated the PR with those changes. Please take a look and let me know if you can think of any other changes needed.

[nicmunroe]

Awesome. Thank you as always!