bash and zsh version, and a few clean-up

* Makefile - let's compile *.c and *.hs with only one command (tested on MacOSX, should also work for Linux)
* prime.bash - bash implementation only using bash internal commands.
* prime.zsh - zsh implementation only using zsh internal commands. (bash ver + sqrt optimization)
* Few clean up:
    - Adds .gitignore
    - Removes a.out
    - Adds shebang (#!) lines and give x bit for the scripts.

Thanks.
-- Ryoichi