don't use an HttpException errorCode anymore, use HttpException sub classes
stronger typing of the HttpException cause
cleaner Http exception fall through
code cleaning
use isTemporaryFailure to detect if an HttpException is severe or not
no more HttpExceptionFactory
rework the handling of the HTTP error data parsing, the data parsed don't need to be an Exception
rename ErrorBody to HttpFailure
just use the ImmutableHttpRequest to parse the error data
No need for the intermediate HttpFailure class, put the error object directly in HttpFailureException
rename httpStatusCode values
no more mention of Plume
Merge remote-tracking branch 'remotes/origin/multi_engine' into multi_engine

Conflicts:
	HttpClient-Ion/src/main/java/com/levelup/http/ion/HttpEngineIon.java
	HttpClient/src/com/levelup/http/AbstractHttpEngine.java
	HttpClient/src/com/levelup/http/HttpException.java
	HttpClient/src/com/levelup/http/internal/HttpEngineUrlConnection.java