remove a.out binary
Give x bit for *.{py,rb,sh} and Makefile for *.{c,hs}

Add shebang line for .py .rb and .sh as well
bash and zsh version using arithmetic exp.
add prime-* (compiled binaries) to .gitignore
Merge pull request #1 from ryo1kato/master

bash and zsh version, and a few clean-up