.save clobbers comments in config

[dgw]

Loaded Sopel, PMed .save, and ran diff. Bit of noise from unrelated testing (for #1688) removed:

--- /home/dgw/.sopel/default.cfg.bak	2019-09-10 17:38:24.848283300 -0500
+++ /home/dgw/.sopel/default.cfg	2019-09-10 17:54:27.508233000 -0500
@@ -1,8 +1,5 @@
-# standalone comment before anything
-
 [core]
 nick = SopelTest
-# comment inside section, between values
 host = irc.rizon.net
 use_ssl = true
 port = 6697
@@ -10,7 +7,6 @@
 enable = 
 	admin
 	reddit
-	# comment in the middle of a value
 	version
 	wikipedia
 	wiktionary
@@ -20,7 +16,6 @@
 channels = 
 
 [wiktionary]
-# standalone comment inside a section
 
 [admin]
 

So that's nice. We're currently (#1687/#1689/#1690) mucking around with ways to avoid ignoring valid config values because of our new, more human-friendly list style (#1628), but this is the other side of that problem: comments getting lost completely when the bot's built-in config editing functions are used. This is a major blocker for #1354, at the very least.

I won't assign this to a milestone just yet. As far as I know, fixing this cleanly would require changing out ConfigParser for a third-party PyPI dependency—something that's not gonna happen for 7.0, certainly. I'm not sure we should do that at all. Maybe this issue is a good argument in favor of switching to YAML? (Probably not.)