Index fixes and performance improvements (fixes #223, #224)

- Fixed creation of duplicate index entries when importing from CurseForge (fixes #224)
- Automatically remove duplicates in index
- Fixed `packwiz serve` with a custom `--pack-root` argument (fixes #223)
- Fixed `packwiz serve` with a custom index.toml location
- Cleaned up internal serving code, added comments and better errors
- Refactored path handling code
- Improved refreshing/exporting performance
- Factored out duplicated exporting logic
- Replaced GetAllMods calls with cleaner LoadAllMods calls and made the former private
- Improved variable names in update command
- Improved handling of aliassed files
- Changed CheckUpdate to take references to metadata
- Removed the ability to use an absolute path to the index file (that probably didn't work anyway)
- Behaviour change: order of entries in exported files may be random

core/interfaces.go

@@ -12,7 +12,7 @@ type Updater interface {
 	ParseUpdate(map[string]interface{}) (interface{}, error)
 	// CheckUpdate checks whether there is an update for each of the mods in the given slice,
 	// called for all of the mods that this updater handles
-	CheckUpdate([]Mod, Pack) ([]UpdateCheck, error)
+	CheckUpdate([]*Mod, Pack) ([]UpdateCheck, error)
 	// DoUpdate carries out the update previously queried in CheckUpdate, on each Mod's metadata,
 	// given pointers to Mods and the value of CachedState for each mod
 	DoUpdate([]*Mod, []interface{}) error