maint: Refactor README

Add background information and some basic concepts of nimsoft so the
goal of the puppet-nimsoft module becomes more clear.
Add helper methods in Puppet::Util::NimsoftSection

The agentil probe configuration (`sapbasis_agentil.cfg`) uses sections
to define arrays like the following:

    <INSTANCE_IPS>
        INDEX000 = 192.168.0.3
        INDEX001 = 192.168.0.4
    </INSTANCE_IPS>

In the nimsoft section this become attributes of the form

    attributes == {
      :INDEX000 => '192.168.0.3',
      :INDEX001 => '192.168.0.4',
    }

Simply calling `attributes.keys` will not return the desired array
because the ordering is non-deterministic (at least in ruby < 1.x).
So create two new methods `keys_in_order` and `values_in_order` that
preserve the original ordering.
Add new type: agentil_landscape

A landscape is the first hierarchy inside the `sapbasis_agentil` probe
GUI and can now be managed as a puppet resource
Add new type: agentil_user

With the `sapbasis_agentil` probe you can define differente user
credentials and then simply assign a user to a system without typing the
username and password dozens of times.

These users can now be defined through puppet with the `agentil_user`
resource.
Add new type: agentil_template

A template defines the monitoring tasks that should apply to a group of
systems or one individual system. Inside the probe GUI you can define
multiple non-system templates and assign one or more template to each
system. Assigning templates to a system will trigger the creation of a
system template that is specific to one system and contains the actual
monitoring rules.

You can now create both types of templates with puppet.
Add new type: agentil_system

systems are the core component of the agentil configuration and each
system contains references to a landscape and to the user that can be
used to connect to the system. A system also includes references to
assigned templates and to the actual system template that contains
the actual monitoring rules.

Systems can now finally be managed through puppet with the
`agentil_system` resource type.
Merge branch 'feature_agentil'

* feature_agentil:
  Add new type: agentil_system
  Add new type: agentil_template
  Add new type: agentil_user
  Add new type: agentil_landscape
  Add helper methods in Puppet::Util::NimsoftSection