added docu for cast expression
added docu for cast expression

aslanbekirov/crate,puneetjaiswal/crate,adrpar/crate,husky-koglhof/crate,sunny256/crate,adrpar/crate,crate/crate,puneetjaiswal/crate,sunny256/crate,EvilMcJerkface/crate,EvilMcJerkface/crate,gmrodrigues/crate,husky-koglhof/crate,gmrodrigues/crate,crate/crate,sunny256/crate,adrpar/crate,husky-koglhof/crate,crate/crate,aslanbekirov/crate,EvilMcJerkface/crate,aslanbekirov/crate,gmrodrigues/crate,puneetjaiswal/crate