Add missing guild information

[TheNullicorn]

The Java API is missing a number of guild features (such as ranks, as pointed out in #463), so this PR aims to add those, as well as refactoring areas of the Java API relating to guilds.

GuildReply.java

• Added documentation
• Made immutable
• Removed unnecessary boxed types (namely Boolean)
• Added equals and hashCode
• Added some missing stats:
  • Guild.getRanks()
  • Guild.getPreferredGames()
  • Guild.getExperienceForGame(GameType) - from web API's guildExpByGameType field
  • Guild.getAchievementHighScore(GuildAchievement) - from web API's achievements field
  • Member.getExperienceEarned(LocalDate) - from web API's members[i].expHistory field ‎
• Renamed some methods (e.g. get_id() -> getId(), getCreated() -> getCreationDate(), etc)
  • Original methods haven't been deleted, just deprecated.
  • Future updates can remove the originals if necessary. ‎
• Fixed some confusing behavior by Guild.getLegacyRanking()
  • Previously, it returned 0 for guilds created after the guild update (those without a ranking)
  • 0 was also used to represent 1st place (for "The Foundation" guild).
  • Now, it returns -1 in those cases.
  • For guilds that did have a ranking, the ranking returned would be zero-based
  • This is no longer the case (1 == 1st place, 2 == 2nd place, and so on)

Banner.java

• Added documentation
• Made immutable
• Added equals and hashCode
• Renamed some methods
  • Banner.getBase() --> Banner.getBaseColor()
  • Pattern.getPattern() --> Pattern.getType()
  • Same as above: the original names were not deleted, just deprecated.

GetGuildExample.java

• Rewritten to better showcase the guild API (and general usage of the Java API)
  • Includes the methods added above
  • Partially copied from GetPlayerExample

GuildAchievement.java

• Created to supplement getAchievementHighScore() in the Guild class
• Used slothpixel/hypixelconstants as a reference

Resolves #463

EDIT

When making this, I purposefully left out 3 fields in particular. The reason for this is that they represent the guild's internal state, and I wouldn't be very surprised if the devs eventually chose to hide/remove them (like they have in the past with certain fields in the "player" endpoint). These fields are:

• guild.chatMute
• guild.members[i].mutedTill
• guild.hideGmTag

If there's any demand for these fields and the devs can confirm that they're intended to be public, I'd be fine adding them. But I'd rather not add them in the first place if there's any chance of them suddenly becoming inaccessible and breaking someone's app.