Refactor Library

The launcher code was in a position ripe for sphagetti, so this rewrites it in a more robust way.
In addition to cleaner code, this provides the following changes:
- Removal of obsolete Mojang authentication
- The rebasing of some internal state into a Sled database
- Tweaks which make some internal mechanisms more robust (e.g. profiles which fail to load can be removed)
- Additional tooling integration such as direnv
- Distinct public API to avoid messing with too much internal code
- Unified error handling in the form of `theseus::Error` and `theseus::Result`

theseus/src/api/mod.rs

@@ -0,0 +1,20 @@
+//! API for interacting with Theseus
+pub mod profile;
+
+pub mod data {
+    pub use crate::{
+        launcher::Credentials,
+        state::{
+            DirectoryInfo, Hooks, JavaSettings, MemorySettings, ModLoader,
+            ProfileMetadata, Settings, WindowSize,
+        },
+    };
+}
+
+pub mod prelude {
+    pub use crate::{
+        data::*,
+        profile::{self, Profile},
+        State,
+    };
+}