Use embedded Ruby, instead of system-wide Ruby.

```
 default["sensu"]["log_directory"]         = "/var/log/sensu"
 default["sensu"]["log_level"]             = "info"
 default["sensu"]["use_ssl"]               = true
-default["sensu"]["use_embedded_ruby"]     = false
+default["sensu"]["use_embedded_ruby"]     = true
 default["sensu"]["init_style"]            = "sysv"
 default["sensu"]["service_max_wait"]      = 10
```

This commit refs #47.
Install gems, using /opt/sensu/embedded/bin/gem.

This commit refs #47.
Use the sensu user's PATH, when using `sudo` command.

This commit refs #47
Delete unnecessary `sudo` command.

This commit refs #47.
Making sure that installing gems via /opt/sensu/embedded/bin/gem after installing sensu.

This commit refs #48.
Change parameters for configurating Twitter gem.

- config.oauth_token        -> config.access_token
- config.oauth_token_secret -> config.access_token_secret

This commit refs #49.
Install `cert.pem` to /opt/sensu/embedded/ssl/cert.pem.

This commit refs #49.
Tweet notification of the first 140 characters.

This commit refs #50.
Install prerequisite gem: net-ping.

This commit refs #46.
Download `check-ping.rb` from Github.

This commit refs #46.
Monitor multiple hosts. Servers are divided into 2 groups:

1. Group 1: Web Servers
2. Group 2: Network Routers

The 1st group is Web Servers. The members are:

- blog
- tech
- jenkins

This group is monitored through HTTP protocol.

The 2nd group is Network Routers. The members are:

- home
- router

This group is monitored through ICMP protocol.

This commit refs #46.
Merge branch 'master' into id/46

Conflicts:
	site-cookbooks/sensu-custom/recipes/prerequisites.rb
Merge branch 'id/46'