Removed CL options.
Avoid GTK L&F.
Create the UnlockedAchievement class.

This commit also adds the time since each achievement was completed.

Achievements should be printed in alphabetical order. AchievementTracker should
sort the UnlockedAchievements according to their ID (as this, hopefully, will
always start the same way as the achievement's name).

Consider implementing insertion sort and using binary search to improve
getUnlockedAchievement() performance.
A little comment.
Three additions to TODO.
Unlocked achievements are now sorted.

Used a TreeSet and a Comparator.

GameData.ACHIEVEMENTS is now a HashMap.
Renamed Command to IssuedCommand.

The reason for this is that in the future I will implement a Command class for
built-in commands.
Refactored the battle method.
Print when a weapon breaks.
Removed unused variable.
Added name element to pom.xml
Removed in-game version string.
Release v0.0.4
Added issueManagement and developers to POM
Limited the size of the CommandHistory.

Used a data structure I named CircularList. It could use some tests.
It is your average ArrayList, but allows you to set a maximum capacity so that
if an element is added after the list is full, the oldest element in the list
gets removed.
The implementation avoids the use of ArrayList.insert() and instead uses a
fake index. This way, after an element is added, just ArrayList.set() is used.