When picking up items, the player should be presented with a menu if multiple items are present

[Lyle-Tafoya]

Currently the player is prompted to confirm pickup for each item, one at a time. This should be replaced by a menu where the player can see a list of the items and corresponding letters, similar to NetHack, DCSS, and other popular roguelikes.

[Lyle-Tafoya]

To help facilitate this, we should probably switch from std::forward_list to std::vector for location::things

[Lyle-Tafoya]

location::things has been switched over to std::vector. Now I just need to stop being lazy and implement the pickup menu.