Ulmo

- raise a friendlier error message for usace.swtwc when no data is found
- bugfix: waterml files with empty metadata elements (e.g. method) were breaking
the parsing logic

- this release includes some backwards incompatible changes
- simplified labels used for KBDI values: kbdi_avg -> avg, kbdi_min -> min...
- added parameter_code kwarg to usgs.nwis.hdf5.get_site_data
- added start and end dates to cuahsi.wof.get_values()
- added support for NCDC's CIRS drought index dataset
- fixed filesystem timestamp related bug that could cause file-based datesets to
be unnecessarily re-downloaded
- version number is now available at ulmo.__version__
- misc documentation fixes

- nwis.pytables has been replaced with nwis.hdf5 which uses the
pandas.io.pytables backend; things should generally run a bit faster now and
the code is much cleaner. There is one backwards-incompatible change:
nwis.hdf5.get_site() is now thread-safe. There was an undocumented behavior
where if a site could not be found in the hdf5 file during a
nwis.pytables.get_site() call, then a request to the NWIS service would be
made and the site table would be updated but no longer happens. You must
explicitly run nwis.hdf5.update_site_list() to update the site list first.
- the nwis.pytables namespace is deprecated in favor of nwis.hdf5 because it is
shorter and more recognizable but pytables is still powering things under the
hood (via the pandas HDFStore)
- parsed timeseries data dicts from waterml-based datasets (cuahsi.wof and
usgs.nwis) now contain parsed site info mapped to the 'site' key
- add support for pre-1997 data from CPC's weekly drought monitor dataset
- bugfix: some related to change of the "current" agricultural year for CPC
weekly drought data
- add support for Texas Weather Connection's Daily Keetch-Byram Drought Index
(KBDI) dataset

- bugfix: interpret missing data ('----') correctly in usace.swtwc.get_stations

- this release includes some backwards incompatible changes
- usgs.nwis date_range parameter has been replaced with more explicit
start, end and period parameters
- ncdc.gsod.get_data() parameters renamed: start_date -> start
and end_date -> end to be consistent with other dataset APIs
- ncdc.gsod.get_stations() now allows limiting stations to matching parameters
(e.g. country='US')
- all date and datetime parameters are now consistently parsed
- added support for CUAHSI's HIS Central service: ulmo.cuahsi.his_central
- added preliminary support for CPC's weekly drought monitor dataset (>=1997)
- added preliminary support for data from USACE Tulsa Water District Control

- this release includes some backwards incompatible changes
- moved module for USGS NWIS from ulmo.usgs -> ulmo.nwis.usgs
- moved module for WaterOneFlow from ulmo.wof -> ulmo.cuahsi.wof