feat(grunt): add custom theme URL support

BREAKING CHANGE: Now you need to set `amsf_theme_url` in `_amsf.yml` before upgrading to the latest version of Almace Scaffolding:

```yaml
amsf_theme_url: https://github.com/amsf/amsf-curtana (or your own if you've already using a custom theme from me)
```

Then you can simply run `grunt update` to process the update. This could be more complex for end users but it also allows users to use custom theme hosted wherever they want.

Gruntfile.coffee

@@ -38,8 +38,9 @@ module.exports = (grunt) ->
         branch: "master"
         assets: "<%= amsf.user.assets %>/themes/<%= amsf.theme.current %>"
         current: "<%= config.amsf.amsf_theme %>"
+        current_url: "<%= config.amsf.amsf_theme_url %>"
         new_name: grunt.option("theme") or "<%= amsf.theme.current %>"
-        new_author: grunt.option("user") or "amsf"
+        new_url: grunt.option("url") or "<%= amsf.theme.current_url %>"
 
     coffeelint:
       options:
@@ -466,7 +467,7 @@ module.exports = (grunt) ->
 
       amsf__theme__add_remote:
         options:
-          repository: "https://github.com/<%= amsf.theme.new_author %>/amsf-<%= amsf.theme.new_name %>.git"
+          repository: "<%= amsf.theme.new_url %>.git"
           branch: "<%= amsf.theme.branch %>"
           directory: "<%= amsf.base %>/themes/<%= amsf.theme.new_name %>/"
 
@@ -504,6 +505,10 @@ module.exports = (grunt) ->
             from: /(amsf_theme: +)(.+)/g
             to: "$1<%= amsf.theme.new_name %>"
           }
+          {
+            from: /(amsf_theme_url: +)(.+)/g
+            to: "$1<%= amsf.theme.new_url %>"
+          }
         ]
 
       amsf__core__update_version:

_amsf.yml

@@ -7,3 +7,4 @@ version:        1.0.1
 
 # Current theme
 amsf_theme:     curtana
+amsf_theme_url: https://github.com/amsf/amsf-curtana