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/error.rs

@@ -0,0 +1,55 @@
+//! Theseus error type
+#[derive(thiserror::Error, Debug)]
+pub enum Error {
+    #[error("Filesystem error: {0}")]
+    FSError(String),
+
+    #[error("Serialization error (JSON): {0}")]
+    JSONError(#[from] serde_json::Error),
+
+    #[error("Serialization error (Bincode): {0}")]
+    EncodeError(#[from] bincode::error::DecodeError),
+
+    #[error("Deserialization error (Bincode): {0}")]
+    DecodeError(#[from] bincode::error::EncodeError),
+
+    #[error("Database error: {0}")]
+    DBError(#[from] sled::Error),
+
+    #[error("Unable to read {0} from any source")]
+    NoValueFor(String),
+
+    #[error("Metadata error: {0}")]
+    MetadataError(#[from] daedalus::Error),
+
+    #[error("I/O error: {0}")]
+    IOError(#[from] std::io::Error),
+
+    #[error("Error launching Minecraft: {0}")]
+    LauncherError(String),
+
+    #[error("Error fetching URL: {0}")]
+    FetchError(#[from] reqwest::Error),
+
+    #[error("Incorrect Sha1 hash for download: {0} != {1}")]
+    HashError(String, String),
+
+    #[error("Paths stored in the database need to be valid UTF-8: {0}")]
+    UTFError(std::path::PathBuf),
+
+    #[error("Invalid input: {0}")]
+    InputError(String),
+
+    #[error(
+        "Tried to access unloaded profile {0}, loading it probably failed"
+    )]
+    UnloadedProfileError(String),
+
+    #[error("Profile {0} is not managed by Theseus!")]
+    UnmanagedProfileError(String),
+
+    #[error("Error: {0}")]
+    OtherError(String),
+}
+
+pub type Result<T> = core::result::Result<T, Error>;