Completely rewrite downloading system

The new system now downloads and decrypts segments individually instead of downloading all segments, merging them, and then decrypting. Overall the download system now acts more like a normal player.

This fixes #23 as the new HLS download system detects changes in keys and init segments as segments are downloaded. DASH still only supports one period, and one period only, but hopefully I can change that in the future.

Downloading code is now also moved from the Track classes to the manifest classes. Download progress is now also actually helpful for segmented downloads (all HLS, and most DASH streams). It uses TQDM to show a progress bar based on how many segments it needs to download, and how fast it downloads them.

There's only one down side currently. Downloading of segmented videos no longer have the benefit of aria2c's -j parameter. Where it can download n URLs concurrently. Aria2c is still used but only -x and -s is going to make a difference.

In the future I will make HLS and DASH download in a multi-threaded way, sort of a manual version of -j.

devine/core/tracks/subtitle.py

@@ -4,7 +4,6 @@ import subprocess
 from collections import defaultdict
 from enum import Enum
 from io import BytesIO
-from pathlib import Path
 from typing import Any, Iterable, Optional
 
 import pycaption
@@ -380,19 +379,6 @@ class Subtitle(Track):
             )
             sub.save()
 
-    def download(self, *args, **kwargs) -> Path:
-        save_path = super().download(*args, **kwargs)
-        if self.codec not in (Subtitle.Codec.SubRip, Subtitle.Codec.SubStationAlphav4):
-            caption_set = self.parse(save_path.read_bytes(), self.codec)
-            self.merge_same_cues(caption_set)
-            srt = pycaption.SRTWriter().write(caption_set)
-            # NowTV sometimes has this, when it isn't, causing mux problems
-            srt = srt.replace("MULTI-LANGUAGE SRT\n", "")
-            save_path.write_text(srt, encoding="utf8")
-            self.codec = Subtitle.Codec.SubRip
-            self.move(self.path.with_suffix(".srt"))
-        return save_path
-
     def __str__(self) -> str:
         return " | ".join(filter(bool, [
             "SUB",