Updated for Zabbix 2.2/2.4 and Slack

- Changed “RECOVERY” to “OK” in comments and scripts
- Changed to using the whole WebHook URL instead of just the token.
- Removed references to $1 and token
Updated README.md

- Added link to Zabbix 2.4 documentation
- Modified to reflect changes in script regarding webhook API
Cleaned up README.md

- Added space on line 58 to match format
- Changed example format
Merge pull request #1 from pdareeves/master

Updated for Zabbix 2.2/2.4 ands new Slack API