Handles file paths and caching.

 st_cached(+File, -Template) is semidet

Retrieves the cached template. Fails when no such template is cached.

 st_cache_invalidate is det

Purges all cache entries.

 st_resolve(+File, -AbsFile, +Options) is det

Resolves file name relative to current working directory. Adds extension.

 st_resolve_include(+Include, +File, -Abs) is det

Resolves included file against the current file. Assumes that File is absolute path.

 st_cache_put(File, Template) is det

Puts the template into cache. Does nothing when caching is not enabled.