Swagger Codegen migration from Mustache and Handlebars templates.

Mustaches and Handlebars use a similar syntax, the implementing changes have been small in order to migrate to handlebars, but there are some details that must be kept in mind.

Here is a list of the main changes done on .mustache files in order to support handlebars:

• To avoid blank spaces between elements we need to use ~ character. This sample {{#elem}} ... {{/elem}} should be used this way: {{#elem}} ... {{/elem~}} to avoid an extra line on the result.

• For {{#-last}} element we should replace the - character with @. We'll need to use: {{#@last}}

The main change that affects templates is that is*, isNot*, has*, hasNot* properties have been removed from codegen pojo (CodegenModel, CodegenProperty, etc) and replaced for extensions. So one option to access those values is: {{#vendorExtension.x-is-enum}}. However we've created handlebar helpers in order to keep using this in a similar way, the sample before can also be expressed this way: {{#is this 'enum'}}, where this references to a codegen pojo in the template.

So these are basically the changes implemented in order to reuse a mustache template in handlebars. I understand that there are more considerations and features in handlebars that can be described, but till now these have been the required changes for migration.