Config Renaming - Use Underscores Consistently

[flatcap]

After a poll on the dev mailing list, we decided to rename a lot of Config Items.

Many names, such as crypt_replyencrypt didn't have _s between words.
This made id hard to remember the formats of config variables.

26 Config items have been renamed (list)
For each one, a config 'synonym' has been created to keep backwards compatibility.

If you have distro-specific config that you'd like to update, you can use this sed script.

sed -i -f config-rename.sed neomutt.rc