Obspycsv

* The same version of obspycsv is included in ObsPy's>=1.5 io.csv module.
Therefore obspycsv will be obsolete with ObsPy>=1.5
* make reading and writing functions private
* make _events2array private, keep public version for backwards compatibility
* depth uses different header for km and m (default dep vs depm)
* removed depth_in_km kwarg in _read_csv
* allow to pass all arguments to Stream.write which are accepted by _write_csv
* use the same order of fields as in EVENTTXT files
* add read support for most EVENTTXT fields
* add load_eventtxt function to load an EVENTXT file into a numpy array
* add write support for EVENTTXT
* improve documentation

* allow to read/write events without depth
* allow to read/write picks without waveformid

* add basic read support for EVENTTXT format (FDSNWS specification)
* use empty string instead of nan/None for missing values
* fix default parameter in read_csv

* add names parameter to read_csv and skipheader paramter to load_csv (consistency between read_csv and load_csv)
* names can be specified as string, sequence or dict

* add load_csv and events2array functions

* allow to write only default csv files with Stream.write()
* allow custom fields for writing
* CSZ files can be read with read_events without specifying check_compression=False for Obspy>=1.4