Initial support for GELF HTTP transport

[joschi]

Closes #9

[coveralls]

Coverage increased (+4.8%) to 84.135% when pulling 56bf286745a581a18993dca12d82d0cc8f7918f1 on gelf-http into c795a5a913ccb93761928fb7fa0d3a2bb632f28f on master.

[coveralls]

Coverage increased (+4.5%) to 87.127% when pulling dcd71d0a014a06213dba984a32b799d2bfe52d04 on gelf-http into a55396ee2287ca859a87714cb8604c94aea8b38e on master.

[CLAassistant]

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1 out of 2 committers have signed the CLA.

:white_check_mark: bernd
:x: Jochen Schalanda

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