Improved util.parse_binary and util_parse_ascii

parse_ascii gained an optional argument (container, defaulting to list)
that indicates the type of the returned value

parse_binary was reverted to previous functioning
Reworked querying for values

- Renamed `ask` to `query` for consistency with othe VISA implementantions
  Added `ask` as alias of `query` for backwards compatibility.
- Added `query_ascii_values` taking an extra paremeter to specify the
  output type.
- Added `query_binary_values` taking an extra paremeter to specify the
  output type. You can also specify the datatype (using the naming of the
  struct module) and the endianess.
- Create a ValuesFormat class to store in an easy way the format specification for the values.
- Added `query_values` which use the values_format attribute.

While the old formatting codes should still work, they will be deprecated in 1.7