Features/erb templates

# What i did

Now snippets can render erb files in place of its body. Usage is described in readme.md:

"Snippets search for templates in RAILS_VIEWS_PATH/shared/snippets. The snippet searchs for a file with its same name but with all non A-Za-z0-9 characters changed to underscores. If this file exists, snippet html body is ignored and the template is rendered in its place".

So I have updated readme.md too, TODO lists included :)

# What I didn't do

I didn''t change versión numbers or any other identification data from the gem.