adds some pages in docs

docs/src/centerselection.md

@@ -11,6 +11,8 @@ KCenters support different ways to compute or select object prototypes (centers)
 You can use them through [`center`](@ref) function; any new scheme must specialize
 from [`AbstractCenterSelection`](@ref) and specialize `center` function.
 
+```@index
+```
 
 ```@docs
 AbstractCenterSelection

docs/src/clustering.md

@@ -9,6 +9,9 @@ end
 
 Functions to cluster objects using distance functions and center selection schemes.
 
+```@index
+```
+
 ```@docs
 ClusteringData
 kcenters

docs/src/criterions.md

@@ -9,6 +9,9 @@ end
 
 The following functions create an stop criterion function of the form: `(dmaxlist, database) -> bool`. This function returns `true` whenever the caller must stop and `false` otherwise.
 
+```@index
+```
+
 ```@docs
 size_criterion
 sqrt_criterion

docs/src/index.md

@@ -7,10 +7,7 @@ CurrentModule = KCenters
 
 ## API
 
-
 ```@index
 ```
 
-```@autodocs
-Modules = [KCenters]
 ```

docs/src/utils.md

@@ -9,6 +9,9 @@ end
 
 Helping functions for partitioning data.
 
+```@index
+```
+
 ```@docs
 partition
 knr