Throttler implementation

[isaachier]

Throttler implementation for Java.

• Adds throttler to avoid debug spans flooding backend.

[codecov[bot]]

Codecov Report

Merging #18 into master will decrease coverage by 0.35%. The diff coverage is 77.67%.

@@             Coverage Diff              @@
##             master      #18      +/-   ##
============================================
- Coverage     84.73%   84.37%   -0.36%     
- Complexity      607      637      +30     
============================================
  Files            94      100       +6     
  Lines          2410     2516     +106     
  Branches        271      284      +13     
============================================
+ Hits           2042     2123      +81     
- Misses          276      292      +16     
- Partials         92      101       +9

Impacted Files	Coverage Δ	Complexity Δ
...-core/src/main/java/com/uber/jaeger/Constants.java	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
...src/main/java/com/uber/jaeger/metrics/Metrics.java	80.43% <ø> (ø)	13 <0> (ø)	:arrow_down:
.../com/uber/jaeger/throttler/ThrottlerException.java	100% <100%> (ø)	1 <1> (?)
...ger-core/src/main/java/com/uber/jaeger/Tracer.java	84.16% <35.71%> (-2.98%)	24 <1> (+1)
...aeger-core/src/main/java/com/uber/jaeger/Span.java	82.17% <42.85%> (-2.51%)	46 <0> (ø)
...com/uber/jaeger/throttler/http/CreditResponse.java	50% <50%> (ø)	1 <1> (?)
...m/uber/jaeger/throttler/http/OperationBalance.java	66.66% <66.66%> (ø)	2 <2> (?)
.../com/uber/jaeger/throttler/HttpThrottlerProxy.java	85.71% <85.71%> (ø)	5 <5> (?)
...e/src/main/java/com/uber/jaeger/TracedProcess.java	87.5% <87.5%> (ø)	3 <3> (?)
...ava/com/uber/jaeger/throttler/RemoteThrottler.java	89.09% <89.09%> (ø)	17 <17> (?)
... and 6 more

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