MAINT: port remaining C modules to Cython in climate, core and timeseries extension modules

[fkuehlein]

There are few remaining functions in those extension modules that are still implemented in C in the respective src_numerics.c files. Porting them to Cython would reduce language diversity of the package and facilitate debugging. Whats more, previous issues listed below have shown that the ports from the legacy weave.inline structure contained errors and should be thoroughly reviewed. This would also help to isolate issues with C compilation, such as #225.

See CHANGELOG.rst for examples:

• CrossRecurrencePlot matrix gives seemingly random values #128
• BUG: Core dump and Segfault when calculating Network.nsi_betweenness() centrality #142
• Segmentation error in Intersystem Recurrence Network #145
• BUG: segfault when calling CouplingAnalysis.mutual_information() and CouplingAnalysis.information_transfer() #187
• MAINT: fully cythonize funcnet.CouplingAnalysis #195