Feature/add docs (#689)

* Add converted docs repo

* Set theme jekyll-theme-minimal

* Removed BC docs, added TOC

* Added TOCs, rewrote most important links in documentation. Linked README to new Github Pages site

* some link fixes

docs/programmers/api-variables/variable-cache-id.md

@@ -0,0 +1,11 @@
+\$cache\_id {#variable.cache.id}
+===========
+
+Persistent cache\_id identifier. As an alternative to passing the same
+`$cache_id` to each and every function call, you can set this
+`$cache_id` and it will be used implicitly thereafter.
+
+With a `$cache_id` you can have multiple cache files for a single call
+to [`display()`](#api.display) or [`fetch()`](#api.fetch) depending for
+example from different content of the same template. See the [caching
+section](#caching) for more information.