Add getter and setter for global FFmpeg options

[iljalukin]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Fixed tickets	fixes #issuenum
Related issues/PRs	#issuenum
License	MIT

What's in this PR?

This PR adds functions to get and set global FFmpeg options.

Why?

These functions are required to set options before the input file argument, for example -hwaccel vaapi for GPU-based encoding.

Example Usage

$video->setOptions(array(
       '-hwaccel', 'vaapi',
       '-hwaccel_output_format' , 'vaapi',
       '-hwaccel_device' , '/dev/dri/renderD128'
));

To Do

• Create tests

[iljalukin]

PR 627 covers the same issue, closing this.