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-lifetime.md

@@ -0,0 +1,30 @@
+\$cache\_lifetime {#variable.cache.lifetime}
+=================
+
+This is the length of time in seconds that a template cache is valid.
+Once this time has expired, the cache will be regenerated.
+
+-   `$caching` must be turned on (either
+    Smarty::CACHING\_LIFETIME\_CURRENT or
+    Smarty::CACHING\_LIFETIME\_SAVED) for `$cache_lifetime` to have any
+    purpose.
+
+-   A `$cache_lifetime` value of -1 will force the cache to never
+    expire.
+
+-   A value of 0 will cause the cache to always regenerate (good for
+    testing only, to disable caching a more efficient method is to set
+    [`$caching`](#variable.caching) = Smarty::CACHING\_OFF).
+
+-   If you want to give certain templates their own cache lifetime, you
+    could do this by setting [`$caching`](#variable.caching) =
+    Smarty::CACHING\_LIFETIME\_SAVED, then set `$cache_lifetime` to a
+    unique value just before calling [`display()`](#api.display) or
+    [`fetch()`](#api.fetch).
+
+If [`$force_compile`](#variable.force.compile) is enabled, the cache
+files will be regenerated every time, effectively disabling caching. You
+can clear all the cache files with the
+[`clear_all_cache()`](#api.clear.all.cache) function, or individual
+cache files (or groups) with the [`clear_cache()`](#api.clear.cache)
+function.