Add In-Memory Repository Support

I am building an application that needs to interact with git (clone repo, create repo, push, etc.) but does not have direct access to a disk. I would like to be able to work with a git repo entirely in-memory.

As an aside, I would also like to be able to work with a git repository that is written out to a non-file datastore such as a database.

In general, it would be nice if the logic in Repository was abstracted out away from the disk. It appears that IRepository is not tightly coupled with disk (assuming all of the various methods that take a path are referring to a relative path). However, there appears to be quite a bit of git specific logic bound up in the Repository implementation which makes it difficult to a novice contributor to implement a custom datastore engine (e.g., in-memory, database, etc.).

Researching this topic very briefly, it appears that the underlying libgit2 supports non-filesystem repositories, so I don't believe this is a technical limitation with libgit2.

先檢視 IRepository 契約與 Repository 實作，接著確認 libgit2 為非檔案系統儲存庫提供了哪些支援。定義記憶體內資料儲存及其他非檔案資料儲存所需的抽象，並透過 clone、create 和 push 等儲存庫操作能在不直接存取磁碟的情況下運作來證明完成。