Add install.sh only for debian
Add service script and configuration file
Make service script executable

it is not executable after download via curl
Add service script and configuration for CentOS
Prevent stopping process
Fix path of droonga-http-server
Fix path of PID file

`droonga-http-server` only works when it's be specified in the full
path.
Add path of PID file option
Add repository

`npm` is't exist in default repository.
Merge pull request #3 from long-long-float/install-script

Add install script for Debian and CentOS7 (WIP)