EventSeries and EventSeriesClimateNetwork

[jakassel]

Pull request to merge new class EventSeries, containing methods for

1. Generating binary event series from time series
2. Event Synchronization, both staticmethod for two event series and implementation for multivariate data
3. Event Coincidence Analysis, both staticmethod for two event series and implementation for multivariate data
4. Significance level computation using Poisson null models for ECA (Donges et al. 2016) and surrogate event series for both ES and ECA.

And class EventSeriesClimateNetwork, inheriting from both EventSeries and ClimateNetwork, to generate climate networks from event series data.