1.0.0-beta6

• added Storage and FilesystemStorage
• renamed Puli\Manager\Api\IOException to Puli\Manager\Api\Storage\StorageException
• replaced PackageFileReader and PackageFileWriter by PackageFileSerializer
• replaced ConfigFileReader and ConfigFileWriter by ConfigFileSerializer
• bindings are now always enabled unless they are explicitly disabled
• removed BindingState::UNDECIDED
• removed InstallInfo::*Enabled*() methods
• improved speed by 99% through optimized SyncRepositoryPath algorithm
• added config key "bootstrap-file" which is loaded before loading plugins
• added repository type "path-mapping"
• added config key "repository.optimize"
• the config key "factory.in.file" can now be set to null if "factory.in.class"
  is auto-loadable
• changed default "repository.type" to "path-mapping"
• added $dev parameter to PackageManager::installPackage()
• added InstallInfo::isDev()