Prevent downloading of a video resolution other than that specified

[axipher]

When using the "-r 1080p" flag, the program should fail to download any resolution of a show that isn't 1080p.

The issue here is that if I've downloaded 90 episodes of an ongoing show like Boruto, then one day 1080p isn't available, then it will go through and download all 90 episodes again at whatever resolution it would find.

[Nicnl]

We have to test it more thoroughly
But I think I fixed this one too along with the resolution issues #86

If the requested resolution is weird from the start, it will just stop:

anime-dl/anime_dl/sites/crunchyroll.py

Lines 203 to 205 in 63d3c74

	if resolution_to_find is None:
	print('Unknown requested resolution %s' % str(resolution).lower())
	return

And finally if the requested resolution is not found in the master.m3u8 file, it will also stop:

anime-dl/anime_dl/sites/crunchyroll.py

Lines 278 to 280 in 63d3c74

	if m3u8_file_text is None:
	print('Could not find the requested resolution %s in the m3u8 file\n' % file_name)
	return