Jdmundrawala/dsc script

@adamedx @btm Here are the changes required to correctly(hopefully?) determine if a dsc requires changing the system state. Piggy-backing with that is improved descriptions for converge_by.

Below is an example run:
The environment var 'dscenv3' does not exist
The file C:\foobar.txt exists
The file C:\foobar1.txt does not exists

The recipe
```ruby
dsc_script 'myenv' do
  code <<-EOH
  environment "env3"
  {
    Name = 'dscenv3'
    Value = 'itsthere'
  }
  EOH
end

dsc_script 'myfile' do
  code <<-EOH
  File OtherFile
  {
      Ensure = "Absent"
      DestinationPath = "C:\\Foobar.txt"
  }
  EOH
end

dsc_script 'myfile1' do
  code <<-EOH
  File OtherFile
  {
      Ensure = "Absent"
      DestinationPath = "C:\\Foobar1.txt"
  }
  EOH
end
```
Chef-client run before this patch
```
Recipe: (chef-apply cookbook)::(chef-apply recipe)
  * [myenv] action run
    - Would DSC resource script for configuration 'myenv'
  * [myfile] action run
    - Would DSC resource script for configuration 'myfile'
  * [myfile1] action run
    - Would DSC resource script for configuration 'myfile1'
```
This is incorrect as [myfile1] should not run since it would not change the state of the system

Chef-client run after this patch
```
Recipe: (chef-apply cookbook)::(chef-apply recipe)
  * [myenv] action run
    - Would DSC resource script for configuration 'myenv'
    - Would  (CREATE) Environment variable 'dscenv3' with value 'itsthere'
  * [myfile] action run
    - Would DSC resource script for configuration 'myfile'
    - Would [C:\Foobar.txt] Deleting the object
  * [myfile1] action run (up to date)
```

Not sure if a lot of people will get that this is some Windows thing -- a comment would help, or we could name it with something that included Windows or PowerShell that are more meaningful to the general developer population.