Resolve conflict

Added ftp service to behavior test.

Resolve conflict

Corrected the .env.example file as it leaked my personal information...

Resolve conflict.

"Cargo.toml":
Hide FTP support under new feature flag.

"operator.rs", "scheme.rs, src/services/mod.rs":
Added conditional compilation for ftp services.

"src/services/ftp/backend.rs":
Removed any unnecessary helper functions that only use
once.
Removed username and password store to avoid data breach.
Combine port and endpoint into one.
Built a FTP command stream inside Builder's build() function
and persist this stream inside Backend.
Changed tls to enable_secure. Developer can use enable_secure() function
to enable tls connection.
Modified read() function to avoid putting all stream content into memory.
Fixed stat() function, when path argument is empty, stat() function will
return the stat of root directory.

"src/services/ftp/dir_stream.rs"
Added more metadata in DirEntry.

"src/services/ftp/err.rs":
Removed any unnecessary error functions.

"src/services/ftp/mod.rs":
Remove empty line.

"tests/behavior/behavior.rs":
Added feature for ftp.

Resolve conflict.

Remove duplicate pattern.

"Cargo.toml":
add services-ftp under example.

Added example section for ftp.

Ignore unaffected vulnerability.

"src/services/ftp/backend.rs":
Added other options insde from_iter() function.
Removed unused code.

"src/services/ftp/backend.rs":
Use resume_transfer() function for offset.

"src/services/ftp/backend.rs":
fixed minor reference bug.

"examples/ftp.rs":
fixed minor reference bug.