Compute a similarity signature for a text file
This walks through the file, only loading a maximum of 4K of file data at
a time. Otherwise, it acts just like git_hashsig_create
.
The path to the input file.
0 on success, GIT_EBUFS if the buffer doesn't contain enough data to compute a valid signature (unless GIT_HASHSIG_ALLOW_SMALL_FILES is set), or error code.