Abs returns absolute path and will expend homedir if path has "~/' prefix.

AbsJoin returns absolute path, and use <dir> as parent dir for relative path.

Exist check if path is exist.

ExpendHome expends path prefix "~/" to home dir.

FindGitWorkSpace walks to upper directories to find gitdir and worktree.

FindTopDir finds repo root path, where has a '.repo' subdir.

HomeDir returns home directory.

IsDir returns true if path is exist and is a directory.

IsFile returns true if path is exist and is a file.

IsGitDir test whether dir is a valid git dir.

SafeCreateParentDir will create parent dir if not exist.

SetHome sets proper HOME environments.

UnsetHome unsets HOME related environments.

DotRepo is ".repo".