This reverts commit 9739700c.

This reverts commit ca5660c4.

Explicitly cache-dir configuration (fixed)

Also create_some_context signature in docs actualized

Revert "Explicitly cache-dir configuration"

Explicitly cache-dir configuration

 - Context constructor: new param cache_dir
 - Program.build actualized: old param cache_dir described with taking into account Context cache_dir

 If not None it will be default one for all context's programs