Change the way the top-level help() message is generated

[tiennou]

This changes generateCliHelp to add a _desc property that can be used to set the name of the "category" the help() command will show for a given object.

This allows mods, like screepsmod-admin-utils to properly show up in the help() command list instead of being earmouthed around.

Said _desc property is either a string, in which case the key it applies to will automatically get () added and the string used as the description for it, or an array of two strings, the first one being the argument names and the second the description.

Example output with some of the mods updated to take advantage of this feature:

> help()
The supported commands are:
* help() - Print this help text.
* print(value) - Print a value to the console.
* storage - A global database storage object.
* map - Map editing functions.
* bots - Manage NPC bot players and their AI scripts.
* strongholds - Manage NPC Strongholds.
* system - System utility functions.
* utils - Extended screepsmod-admin-utils commands
* setPassword(username, password) - Reset a user's password
* mongo - MongoDB management commands
Type help(object) to learn more about specific usage of the object.
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