Fix clang compilation issues

Some of them still remain, but I cannot find a proper way to fix them,
and g++ seems happy.
import extended slices performances
Update TODO list
Enable definition of function with the same name than an intrinsic
Fix len for tuple

* std::tuple doesn't have ::iterator type attributs
Fix zip if all operator doesn't have the same size
In operator for sliced_string in string
Improve string interface

* split, startswith and endswith
Add file type information
Handle slice of slice for string and negative indexing
Fix imap != operator
WIP