Feature: Support for the user to give custom indices for frame selection in addition to the default modes available.

[MrinalJain17]

Internally, the _read_video() function gets an array to indices of frames to be read from a function called _get_frame_indices().

In addition, the user should be able to:

1. Pass an array/list of indices indicating the frames to be extracted.
2. Pass a custom function that will return an array of indices - the input(s) made available to the function will be the same as that of _get_frame_indices()

[MrinalJain17]

Support for custom frame selection will be made available in the next release of mydia- 2.0 (#14 )

Detailed examples will be demonstrated in the documentation subsequently.