Add submission handling and prepare for the v0.3.0 release

Add handling of submissions to subreddits. To achieve this, there are now
two distinct classes for all the logic pertaining to submissions and
comments. On start, the bot forks. The child process takes care of
submissions, while the parent process takes care of comments. Prepare
for the v0.3.0 release of the bot by bumping the version number in
the sample configuration file. Update the documentation and changelog
accordingly.

.gitignore

@@ -1,2 +1,3 @@
 *.ini
 processed_comments_*.txt
+processed_submissions_*.txt

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [0.3.0] - 2018-03-29
+### Added
+- The bot now also handles submissions.
+- Added an option `--prosfile` to control where the bot stores the IDs of
+  processed submissions. The default is `processed_submissions_SUBREDDIT.txt` in
+  the bot's working directory. The submissions file will be kept to a maximum
+  of 500 processed submissions.
+
 ## [0.2.0] - 2017-10-31
 ### Added
 - Added an option `--procfile` to control where the bot stores the IDs of

MaxGoldtBot.ini.sample

@@ -1,6 +1,6 @@
 [MaxGoldtBot]
 client_id=
 client_secret=
-user_agent=python:de.erixpage.maxgoldtbot:v0.2.0 (by /u/pille1842)
+user_agent=python:de.erixpage.maxgoldtbot:v0.3.0 (by /u/pille1842)
 username=
 password=