Front matter scripts

[kmcgrath]

Allows scripts to be referenced in front matter that set template variables.

For instance, get a list of availability zones to loop through to create a maximum number of subnets.

---
subnets:  
  script: subnets
  args:
    - allAZ 
---

subnets.js would live in a particle directory and would be run when frontmatter is read.

Later in the template

{{#each subnets}}
{{!-- will loop over all available AZs for the region being deployed to --}}
{{/each}}

Things to decide:

How should the frontmatter be formatted for these scripts?

What should the particle name be for these scripts?

How should arguments be passed?