enable streaming as XML

[Flet]

• refactored api.stream.service.js: moved JSON streaming to its own file

• For xml format, the stream will return buffers, so each data chunk will be a buffer filled with exactly one object (example: <product><sku>123</sku></product>)

• If streaming xml directly into a file, be sure to add the xml pragma and wrap the stream in a root element or it won't be valid.

• xml format is not supported by the openBox endpoint

[coveralls]

Coverage decreased (-3.03%) to 96.61% when pulling 15c8065 on stream-as-xml into fefc361 on master.

[coveralls]

Coverage decreased (-1.6%) to 98.045% when pulling cd95756 on stream-as-xml into fefc361 on master.

[coveralls]

Coverage decreased (-1.6%) to 98.039% when pulling 25beee8 on stream-as-xml into fefc361 on master.

[coveralls]

Coverage decreased (-1.6%) to 98.039% when pulling 25beee8 on stream-as-xml into fefc361 on master.

[coveralls]

Coverage increased (+0.08%) to 99.72% when pulling 07b943a on stream-as-xml into fefc361 on master.

[coveralls]

Coverage increased (+0.08%) to 99.72% when pulling 07b943a on stream-as-xml into fefc361 on master.