all: cut bloated HTTP-client and tuning options

This is a personal torrent client, not a web client or daemon, so the
rarely-used HTTP-client knobs and redundant tuning flags are gone — flag,
config field, implementation, and tests removed for each. The option
surface drops from 54 to 28.

Web-client cluster removed: --all-proxy (HTTP_PROXY env still works),
load/save-cookies, --referer, -U/--user-agent, --http-user/--http-passwd,
--conditional-get, --remote-time, --check-certificate, --ca-certificate,
--lowest-speed-limit. Pass --header for a one-off auth/cookie/UA header.

Redundant knobs removed: -x and -k (folded into -s), --connect-timeout,
--retry-wait, per-item --max-download-limit/-u, --bt-max-peers,
--bt-stop-timeout, --disable-ipv6, --auto-save-interval, --human-readable,
--stop, -T (a positional .torrent works). follow-torrent and human-readable
are now unconditional defaults.

README.md

@@ -2,7 +2,9 @@
 
 A command-line download tool in Go. It fetches HTTP(S) files over multiple
 connections and downloads BitTorrent magnets and `.torrent` files — one binary,
-familiar flags.
+a small set of flags. It is a downloader, not a web client: there are no
+cookie/proxy/auth flags — pass `--header` for a one-off header (auth token,
+cookie, user-agent) when a download needs one.
 
 ## Build
 
@@ -22,10 +24,9 @@ got -s16 https://example.com/big.iso
 # resume an interrupted download
 got -c https://example.com/big.iso
 
-# one file from several mirrors (connections spread across servers,
+# one file from several mirrors (segments spread across the servers,
 # a dead mirror falls over); -Z downloads them as separate files instead.
-# -x caps connections per server when mirroring.
-got -s16 -x4 https://a.example/big.iso https://b.example/big.iso
+got -s16 https://a.example/big.iso https://b.example/big.iso
 
 # a torrent or magnet; seed for 30 minutes after finishing
 got --seed-time=30 ubuntu.torrent
@@ -45,7 +46,6 @@ Run `got --help` (or `--help=all`) for every option.
 | `-o, --out` | output filename | from URL |
 | `-c, --continue` | resume a partial download | false |
 | `-s, --split` | connections per download (the speed dial) | 5 |
-| `-x, --max-connection-per-server` | cap connections per server (1–16) | 1 (= split when unset) |
 | `-j, --max-concurrent-downloads` | files downloaded at once | 5 |
 | `--max-overall-download-limit` | global speed cap | 0 (off) |
 | `--checksum` | verify the finished file: `TYPE=DIGEST` (sha-256, sha-1, …) | |
@@ -69,6 +69,6 @@ got -c --save-session=got.session -i got.session  <urls/magnets...>
 - BitTorrent uses [`anacrolix/torrent`](https://github.com/anacrolix/torrent);
   HTTP uses the standard library.
 - Not implemented: FTP/SFTP, Metalink, and the JSON-RPC server.
-- When several torrents run at once, `--max-download-limit` /
-  `--max-upload-limit` apply per run rather than per torrent (`--max-overall-*`
-  are exact).
+- Speed caps are global: `--max-overall-download-limit` /
+  `--max-overall-upload-limit` apply across the whole run.
+- Standard `HTTP_PROXY` / `HTTPS_PROXY` environment variables are honored.