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/pack.go

@@ -110,9 +110,6 @@ func (pack *Pack) UpdateIndexHash() error {
 
 	fileNative := filepath.FromSlash(pack.Index.File)
 	indexFile := filepath.Join(filepath.Dir(viper.GetString("pack-file")), fileNative)
-	if filepath.IsAbs(pack.Index.File) {
-		indexFile = pack.Index.File
-	}
 
 	f, err := os.Open(indexFile)
 	if err != nil {