Add fig.subplot and fig.sca to API docs

Also updated tutorial a bit

Author: weiji14

doc/api/index.rst

@@ -34,7 +34,9 @@ Plotting data and laying out the map:
     Figure.legend
     Figure.logo
     Figure.image
+    Figure.sca
     Figure.shift_origin
+    Figure.subplot
     Figure.text
     Figure.meca
 

examples/tutorials/subplots.py

@@ -62,11 +62,11 @@
 fig.show()
 
 ###############################################################################
-# The ``fig.sca`` command activates a specified subplot, and all subsequent
-# plotting commands will take place in that subplot. This is similar to
-# matplotlib's ``plt.sca`` method. In order to specify a subplot, you will need
-# to provide the identifier for that subplot via the ``ax`` argument. This can
-# be found in the ``axs`` variable referenced by the ``row`` and ``col``
+# The :meth:`pygmt.Figure.sca` command activates a specified subplot, and all
+# subsequent plotting commands will take place in that subplot. This is similar
+# to matplotlib's ``plt.sca`` method. In order to specify a subplot, you will
+# need to provide the identifier for that subplot via the ``ax`` argument. This
+# can be found in the ``axs`` variable referenced by the ``row`` and ``col``
 # number.
 
 ###############################################################################
@@ -235,4 +235,4 @@
 ###############################################################################
 # Since we skipped the second subplot, the auto label function will name the
 # three subplots as a, c and d, which is not what we want, so we have to use
-# ``fig.sca(A=""(a)"`` to manually set the subplot label.
+# ``fig.sca(autolabel=""(a)"`` to manually set the subplot label.