Apsg

* RTD fix

* Added E1,E2,E3 properties and polar decomposition method to DefGrad object
* StereoNet has vector method to mimics lower and upper hemisphere plotting
of Lin and Vec3 objects as used in paleomagnetic plots
* StereoNet could be initialized with subplots
* rake method of Fol added to return vector defined by rake
* Density could be initialized without data for user-defined calculations
New method apply_func could be used to calculate density
* Contour(f) methods accept Density object as argument
* Added Group class methods to generate Spherical Fibonacci and Golden Section
based uniform distributions of Vec3, Lin and Fol

* FabricPlot - triangular fabric plot added
* .asvec3 property has .V alias
* Resultant of Fol and Lin is calculated as vectorial in centered position
* dv property of Fol added to return dip slip vector

* SDB class improved. Support basic filtering including tags
* StereoNet has close method to close figure and new method
to re-initialize figure when closed in interactive mode
* iapsg shell script added to invoke apsg ipython shell

* Group fancy indexing implemented. Group could be indexed by sequences
of indexes like list, tuple or array as well as sliced.
* Cluster class with hierarchical clustering implemented
* Group to_file and from_file methods implemented to store data in file
* Group copy method for shallow copy implemented
* StereoNet now accept Vec3 and Fault object as well for instant plotting.
* Ortensor updated with new properties E1,E2,E3 and Vollmer(1989) indexes
P,G,R and C. Bug in Woodcocks's shape and strength values fixed.
* uniform_lin and uniform_fol improved.
* asvec3 method implemented for Fol and Lin
* fol_plot property of StereoNet allows choose poles or great circles for
immediate plotting
* bootstrap method of Group provide generator of random resampling with
replacements.
* Group examples method provide few well-known datasets.
* Matplotlib deprecation warnings are ignored by default

* New Docstrings format
* StereoNet.getfols method bug fixed.
* Shell scripts to run interactive session improved.