add client keepalive publish timing

Adding that clients send keepalive data every 20 seconds.

Changing example client config as the threshold was not technically possible at 10 seconds.

https://github.com/sensu/sensu/blob/master/lib/sensu/client.rb#L69
Merge pull request #77 from agent462/patch-2

add client keepalive publish timing
Added CentOS bootup instructions
Adjusted to create Start the RabbitMQ server section
Merge pull request #78 from VitaliyBSD/master

Added CentOS bootup instructions
Fix incorrect link to api-clients
Merge pull request #79 from cwjohnston/patch-1

Fix incorrect link to api-clients in 0.11 docs
Adding aggregate check documentation.

Only the APIs for aggregates is in the docs. How to setup an aggregate check is not.
Fixing typo in handlers.md (missing closing quote)
Fixing typo in handlers.md (missing closing quote)
Merge pull request #84 from aleszoulek/patch-1

Fixing typo in handlers.md (missing closing quote)
Merge pull request #80 from soule047/patch-1

Adding aggregate check documentation.
type, should use by instead of be
Merge pull request #86 from slyness/spelling_correction

type, should use by instead of be
Fix italics caused by variable name.
Update installing_sensu.md

Dashboard service may not be on the same host as API, so note the required connectivity.
Merge pull request #89 from jhmartin/patch-2

Update installing_sensu.md
Merge pull request #88 from grepory/patch-1

Fix italics caused by variable name.
[epel] corrected epel dl url for centos 5/6, for sensu 0.11.x and 0.12.x
Merge pull request #91 from portertech/epel

corrected epel dl url for centos 5/6, for sensu 0.11.x and 0.12.x