Following the Don't Repeat Yourself principle, define macros
for the structures that contain the request and response headers,
so that the name is not repeated in multiple places in multiple files.
https://bugzilla.gnome.org/show_bug.cgi?id=762144
To allow code from dash_demux.c to be used by other elements
that are based upon GstAdaptiveDemux, the code has been
refactored into four new files:
adaptive_demux_engine.[ch]
adaptive_demux_common.[ch]
The code in adaptive_demux_engine.c provides a generic
test engine for elements based upon GstAdaptiveDemux.
The code in adaptive_demux_common.c provides a set
of utility functions that are common between the tests
for hlsdemux and dashdemux.
As part of the refactoring, variables in structures were
renamed from using camelCase to underscore_case to match other
GStreamer source code.
The fake_http_src was renamed test_http_src and changed to use
callbacks to provide input data and error conditions. Rather than
using an array of input data that tries to encode all the
possible use cases for the GstTestHTTPSrc element, use a struct of
callbacks.
Users of this element are obliged to implement at least the src_start
callback, which provides a way to link from a URI to the settings
for that URI.
