add drop_sel, drop_vars, map to api.rst (#3506)

doc/api.rst

@@ -94,7 +94,7 @@ Dataset contents
    Dataset.rename_dims
    Dataset.swap_dims
    Dataset.expand_dims
-   Dataset.drop
+   Dataset.drop_vars
    Dataset.drop_dims
    Dataset.set_coords
    Dataset.reset_coords
@@ -118,6 +118,7 @@ Indexing
    Dataset.loc
    Dataset.isel
    Dataset.sel
+   Dataset.drop_sel
    Dataset.head
    Dataset.tail
    Dataset.thin
@@ -154,7 +155,7 @@ Computation
 .. autosummary::
    :toctree: generated/
 
-   Dataset.apply
+   Dataset.map
    Dataset.reduce
    Dataset.groupby
    Dataset.groupby_bins
@@ -263,7 +264,7 @@ DataArray contents
    DataArray.rename
    DataArray.swap_dims
    DataArray.expand_dims
-   DataArray.drop
+   DataArray.drop_vars
    DataArray.reset_coords
    DataArray.copy
 
@@ -283,6 +284,7 @@ Indexing
    DataArray.loc
    DataArray.isel
    DataArray.sel
+   DataArray.drop_sel
    DataArray.head
    DataArray.tail
    DataArray.thin
@@ -542,10 +544,10 @@ GroupBy objects
    :toctree: generated/
 
    core.groupby.DataArrayGroupBy
-   core.groupby.DataArrayGroupBy.apply
+   core.groupby.DataArrayGroupBy.map
    core.groupby.DataArrayGroupBy.reduce
    core.groupby.DatasetGroupBy
-   core.groupby.DatasetGroupBy.apply
+   core.groupby.DatasetGroupBy.map
    core.groupby.DatasetGroupBy.reduce
 
 Rolling objects
@@ -566,7 +568,7 @@ Resample objects
 ================
 
 Resample objects also implement the GroupBy interface
-(methods like ``apply()``, ``reduce()``, ``mean()``, ``sum()``, etc.).
+(methods like ``map()``, ``reduce()``, ``mean()``, ``sum()``, etc.).
 
 .. autosummary::
    :toctree: generated/