Since the example files are not executable binaries, this PR removes the shebangs.
This ensures that all examples are consistently executed via `ruby` command.
It also removes the executable permission from `examples/stdio_server.rb` using `chmod 444`,
bringing it in line with the other example files.
This PR renamed the files related to the SSE example and fixed the README.md.
Because missing files were specified in README.md.
And also, I removed the word 'test' from the file names related to the SSE example.
Other examples file names do not contain the word `test`.
