- changed handling of zip files in REST query
- DSD.code is now a dictionary
DSD: remove dot from names of codes
added key for Data series; fixed bug introduced in previous commit
Change type of time_series.

As dr-leo said on github:
"A dict with keys generated by uuid is useless as the keys are
meaningless and not human-friendly. Why not use a list instead?"
A dict with ramdomly generated keys is incredibly stupid and could
deserve a place on thedailywtf.com.
Fix typo
Make some classes accessible from SDMX_REST

It makes subclassing easier.
Prettier path construction (kudos should go to dr-leo)
Fix typos and stupid bugs
Add docstrings
Refactor a large part of the code. Implement SDMX 2_0

We now support ILO and ECB
accelerated data_extraction for SDMX version 2.1 by traveling the xml
tree only once.
put codes in OrderedDict. Thanks to dr-leo for suggesting it.
adding provision for test server on localhost. Test datafiles
manually downloaded from provider must be stored in /var/www/pysdmx in
conforming sub-directories. A configuration of nginx server is
provided in nginx_test_server.
Change the data structure as suggested by dr-leo.
Change name to sdmx
Convert dtype object to float64
Update README