maxComments is now only the user-preferred setting, and has nothing to
do with displayed state. loadingMoreComments is used to trigger loading
more comments, and temporarily contains the desired comment count to
load. This should make future changes easier. Also fix two minor bugs:
* the 'Reload' was sometimes hidden after clicking 'load more comments'
* 'loaded x more comments' incorrectly appeared after clicking 'Reload'
Beforehand, Pushshift comments were all downloaded first, then they were
processed, then all Reddit comments were downloaded, then processed.
Now, as each batch of Pushshift comments completes, it is processed
asynchronously, and Reddit comments are downloaded & processed as soon
as enough comment IDs have been batched for submission. This minimizes
the amount of time spent in the 'Comparing comments to Reddit API'
phase. It also spaces out Reddit API requests for better netiquette.
* only rerender the comments after loading and iff something changes
* change text to 'loading...' and make link unclickable while waiting
* if all comments are already loaded, rename to 'load new comments'
Also update the reddit endpoint for posts, and add the capability
to download from Pushshift in multiple batches, with a binary
backoff; it's currently set to download up to 1,000 comments.
Credit (once again) to @ayan4m1 for a couple snippets of code.
