new code-base with PSR standards

[voku]

Hi, I forked this project some time ago, because I wanted to lean something from other devs code, in the mean time, I added some features that maybe helpfull for others also. :)

new features:

• PSR-3: Logger Interface
• PSR-7: HTTP Message Interface
• PSR-17: HTTP Factory Interface
• PSR-18: HTTP Client Interface
• support for async requests

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This change is 

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@a29ca5c). Click here to learn what that means. The diff coverage is 62.78%.

@@            Coverage Diff            @@
##             master     #282   +/-   ##
=========================================
  Coverage          ?   64.51%           
  Complexity        ?     1093           
=========================================
  Files             ?       27           
  Lines             ?     2725           
  Branches          ?        0           
=========================================
  Hits              ?     1758           
  Misses            ?      967           
  Partials          ?        0

Impacted Files	Coverage Δ	Complexity Δ
src/Httpful/Request.php	67.89% <ø> (ø)	347 <0> (?)
src/Httpful/Exception/ClientErrorException.php	0% <0%> (ø)	7 <7> (?)
src/Httpful/Proxy.php	0% <0%> (ø)	0 <0> (?)
src/Httpful/Handlers/JsonMimeHandler.php	100% <100%> (ø)	7 <7> (?)
src/Httpful/Handlers/AbstractMimeHandler.php	100% <100%> (ø)	1 <1> (?)
src/Httpful/ClientMulti.php	15.2% <15.2%> (ø)	37 <37> (?)
src/Httpful/Handlers/XmlMimeHandler.php	16.66% <16.66%> (ø)	23 <23> (?)
src/Httpful/Factory.php	28.57% <28.57%> (ø)	12 <12> (?)
src/Httpful/Handlers/CsvMimeHandler.php	36% <36%> (ø)	9 <9> (?)
src/Httpful/UriResolver.php	39.21% <39.21%> (ø)	54 <54> (?)
... and 17 more

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