Gen refactor

[boynton]

Matches the refactor done in ardielle-go. Removed the model generator from this repo, replaced by references to ardielle-go.

[dmitris]

I'm seeing this gofmt problem (spacing issue):

$ gofmt -l .
rdl-plugins/markdown/rdl-gen-markdown/main.go
$ gofmt -d .
diff -u rdl-plugins/markdown/rdl-gen-markdown/main.go.orig rdl-plugins/markdown/rdl-gen-markdown/main.go
--- rdl-plugins/markdown/rdl-gen-markdown/main.go.orig  2018-08-23 09:32:50.000000000 +0200
+++ rdl-plugins/markdown/rdl-gen-markdown/main.go   2018-08-23 09:32:50.000000000 +0200
@@ -226,7 +226,7 @@
 }

 type entry struct {
-   name string
+   name      string
    resources []*rdl.Resource
 }

[boynton]

True, but that is unrelated to this PR. Might be worth opening an issue for go fmt in general

[dmitris]

( I fixed the gofmt issue in master in #101 )