Add development doc

Author: Joan Massich

doc/developers_utils.rst

@@ -0,0 +1,39 @@
+.. _developers-utils:
+
+========================
+Utilities for Developers
+========================
+
+Imbalanced-learn contains a number of utilities to help with development.  These are
+located in :mod:`imblearn.utils`, and include tools in a number of categories.
+All the following functions and classes are in the module :mod:`imblearn.utils`.
+
+.. warning ::
+
+   These utilities are meant to be used internally within the imbalanced-learn
+   package.  They are not guaranteed to be stable between versions of
+   scikit-learn.  Backports, in particular, will be removed as the scikit-learn
+   dependencies evolve.
+
+
+.. currentmodule:: imblearn.utils
+
+
+Validation Tools
+================
+
+These are tools used to check and validate input.  When you write a function
+which accepts arrays, matrices, or sparse matrices as arguments, the following
+should be used when applicable.
+
+- :func:`check_neighbors_object`: Check the objects is consistent to be a NN.
+- :func:`check_target_type`: Check the target types to be conform to the current samplers.
+- :func:`check_ratio`: Checks ratio for consistent type and return a dictionary
+    containing each targeted class with its corresponding number of pixel.
+
+Helper Functions
+================
+These are tools to facilitate writing code for imbalance learn.
+
+- :func:`hash_X_y`: Compute hash of the input arrays.
+- :func:`deprecate_parameter`: Helper to deprecate a parameter by another one. 

doc/user_guide.rst

@@ -15,3 +15,4 @@ User Guide
    combine.rst
    ensemble.rst
    Dataset loading utilities <datasets/index.rst>
+   developers_utils.rst