Alias continuous (Z) for makecpt

Included one test to create a continuous cpt from blue to white. Also updated link to the full list of GMT's color palette tables due to documentation reorganization during GenericMappingTools/gmt#1594.

pygmt/mathops.py

@@ -7,7 +7,7 @@
 
 
 @fmt_docstring
-@use_alias(C="cmap", T="series", G="truncate", H="output", I="reverse")
+@use_alias(C="cmap", T="series", G="truncate", H="output", I="reverse", Z="continuous")
 @kwargs_to_strings(T="sequence", G="sequence")
 def makecpt(**kwargs):
     """
@@ -20,7 +20,7 @@ def makecpt(**kwargs):
     cmap (C) : str
         Selects the master color palette table (CPT) to use in the interpolation.
         Full list of built-in color palette tables can be found at
-        :gmt-docs:`GMT_Docs.html#built-in-color-palette-tables-cpt`.
+        :gmt-docs:`cookbook/cpts.html#built-in-color-palette-tables-cpt`.
 
     series (T) : list or str
         ``[min/max/inc[+b|l|n]|file|list]``.
@@ -46,6 +46,12 @@ def makecpt(**kwargs):
         the latter must be compatible with the changed z-range. See also
         :gmt-docs:`cookbook/features.html#manipulating-cpts`.
 
+    continuous (Z) : bool
+        Creates a continuous CPT [Default is discontinuous, i.e., constant colors for
+        each interval]. This option has no effect when no -T is used, or when using
+        -Tz_min/z_max; in the first case the input CPT remains untouched, in the second
+        case it is only scaled to match the range z_min/z_max.
+
     {aliases}
     """
     with Session() as lib:

pygmt/tests/test_makecpt.py

@@ -163,3 +163,15 @@ def test_makecpt_reverse_color_and_zsign(grid):
     makecpt(cmap="earth", reverse="cz")
     fig.grdimage(grid, projection="W0/6i")
     return fig
+
+
+@pytest.mark.mpl_image_compare
+def test_makecpt_continuous(grid):
+    """
+    Use static color palette table that is continuous from blue to white and scaled from
+    -4500 to 4500m.
+    """
+    fig = Figure()
+    makecpt(cmap="blue,white", continuous=True, series="-4500,4500")
+    fig.grdimage(grid, projection="W0/6i")
+    return fig