Fixed typo in CONTRIBUTING

Parenthetical belonged in the sentence.

Fixes #1139.
updated to add international@reddit.com
clarified who to contact about submission problems

clarified that people should contact the subreddit mods about submissions

Fixes #1036.
It's not needed to invoke bash with the -e option.

This patch is super simple :) Basically, the first command of the
install-reddit.sh file is "set -e". Therefore, we don't have to invoke bash
with "#!/bin/bash -e". We can either remove the -e from the "#!/bin/bash -e" or
we can remove "set -e". I prefer keeping "set -e" because it's more explicit.

Fixes #1033.
Corrects capitalization

Corrects capitalization in CONTRIBUTING.md

Fixes #1006.
Added missing period

Following the style of contributor and moderator messages, the subscriber
message should also have a period at the end.

Fixes #974.
Add _ to list of valid hostname characters

This is in response to https://github.com/reddit/reddit/issues/289

Fixes #929.