Feature_methods dictionary

[belevtsoff]

@btel

possible solution to #78

changes:

• feature_methods is now OrderedDict()
• feature naming convention is now method_name:channel(optional):feature_name
• clearer names for PCA and WT methods
• optional argument feat_method_names for features.combine

[btel]

could you update the code example in https://github.com/btel/SpikeSort/blob/feature_methods_dict/docs/source/datastructures.rst to reflect changes in future labels?

[belevtsoff]

@btel

could you update the code example

low level fet* methods are not changed, because they are not aware whether they are used once or twice. So it only makes sense to prepend feature names with method names in the high-level API context. Therefore, the aforementioned example yields same results as before