Added -filter_complex argument filter to FFmpeg Stream Builder

[matthewjt]

Added -filter_complex argument filter to FFmpeg Stream Builder
Resolved error in ExamplesTest

[coveralls]

Changes Unknown when pulling 1643aa5 on matthewjt:video_filter_complex into ** on bramp:master**.

[bramp]

The change looks good. A couple of comments/questions

1. Please add a test case, to ensure this continues to work in the future.

2. Can the -complex_filter flag per used once per output, or only once? As implemented it looks like we can do:

FFmpegBuilder builder = new FFmpegBuilder()
  .setInput("input.avi")
  .addOutput("output1.mp3")
    .setComplexFilter("...")
  .addOutput("output2.mp3")
    .setComplexFilter("...")

Is that valid? I suspect ComplexFilter is only allowed to be invoked once? Thus it might be better to move it to the FFmpegBuilder? But I'm not sure I fully understand the semantics of this flag.

[matthewjt]

Wow you're right. It should only be set once. I went to move it into the FFmpegBuilder and found that it already exists there! I guess we don't need this pull request after all.

[bramp]

Oh great, sorry I didn't realise that before. Happy to receive contribution in future.