Adding support for ttl by column in insert

I've done a little improvement on my previous code:
* Add a new function "get_ttl" that return a ttl from a ttl array or an int (refactoring)
* Add support for ttl in the insert function. You can now  add a ttl by column, just pass an array TTL: ('column_name1' => 'ttl_column1',...)
* You can now use a TTL array smaller than the column (or row) array. Column (or row) that does not have a matching ttl will not use TTL.