Add Static Proxy Interface & Refactor Test Suites

[gfargo]

This PR performs a major overhaul on how you interface with the NewsAPI library.

• Creates Client class, a static proxy class, to simplify library interactions
• Separates concerns into traits & abstract classes
• Adds test class for each class in library

[codecov[bot]]

Codecov Report

Merging #4 into master will increase coverage by 29.41%. The diff coverage is 100%.

@@             Coverage Diff             @@
##             master     #4       +/-   ##
===========================================
+ Coverage     70.58%   100%   +29.41%     
- Complexity        8     20       +12     
===========================================
  Files             1      4        +3     
  Lines            17     46       +29     
===========================================
+ Hits             12     46       +34     
+ Misses            5      0        -5

Impacted Files	Coverage Δ	Complexity Δ
src/Client.php	100% <100%> (ø)	7 <7> (?)
src/traits/RemoteHeaders.php	100% <100%> (ø)	2 <2> (?)
src/v2/Adapter.php	100% <100%> (ø)	7 <7> (?)
src/traits/RemoteEndpoints.php	100% <100%> (ø)	4 <4> (?)

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