Modification in indexed_array implementation
Improve gslice interface

* operator[]
* operator+=
* operator/=
* improve at performance
Fix islice

* avoid dangling reference (same issue than in imap b45f10ad2a28bd4fec027bd0a848304fb1d34663)
keep cpp files when compilation failed

* needed and really usefull for debug
export sliced string to python
Handle case of empty string
Add tests

* Many test from rosetta and for numpy
Fix assignment of gsliced_array