add template processing builtin

[coryb]

adding a basic templating function. can be used like:

string secretPath() {
  template <<-EOM
    {{- if . -}}
      /path/to/ci/secret
    {{- else -}}
      /path/to/user/secret
    {{- end -}}
  EOM string {
    localEnv "CI"
  }
}

The part I don't like about this is the argument data into the template. The PR currently passes the variadic arguments as a []string slice when there is more than one argument to template, otherwise it will pass just a single string argument if only 1 variadic arg. I am not sure there is a more logical approach. If we wanted to pass named arguments to allow for {{ .name }} we would have to have some syntax that supports maps, which we dont have yet.

[hinshun]

An alternative is to use with option like a map. For example:

string secretPath() {
  template <<-EOM
    {{- if .CI -}}
      /path/to/ci/secret
    {{- else -}}
      /path/to/user/secret
    {{- end -}}
  EOM with option {
        stringField "CI" string { localEnv "CI"; }
  }
}

[hinshun]

@param needs to be followed by text

[coryb]

fixed

[coryb]

string secretPath() {
  template <<-EOM
    {{- if .CI -}}
      /path/to/ci/secret
    {{- else -}}
      /path/to/user/secret
    {{- end -}}
  EOM with option {
        stringField "CI" string { localEnv "CI"; }
  }
}

I thought about it a while, I think this makes the most sense. It will be less cumbersome when we fix #100 and I think it provides flexibility going forward.

I will update the PR for option::template

[coryb]

@hinshun updated PR with option::template

[hinshun]

Ship it!