Wrap triangulate (GenericMappingTools#731)

Wrapping the triangulate function which does
"Delaunay triangulation or Voronoi partitioning
and gridding of Cartesian data".
Original GMT documentation can be found at
https://docs.generic-mapping-tools.org/6.3/triangulate.html.

Aliased outgrid (G), spacing (I), projection (J),
region (R), verbose (V), registration (r).

* Refactor triangulate to use virtualfile_from_data
* Refactor triangulate implementation to use pygmt.io.load_dataarray
* Alias binary(b), nodata(d), find(e), coltypes(f), header(h), incols(i)

* Rename the parameter 'table' to 'data'

As per GenericMappingTools#1479.

* Refactor test_triangulate to use Table_5_11_mean.xyz instead of tut_ship
* Refactor test_triangulate_with_outgrid to use xr.testing.assert_allclose
* Refactor test_triangulate_input_xyz to use pd.testing.assert_frame_equal

* Implement regular_grid and delaunay_triples staticmethod for triangulate
* Let list inputs to spacing (I) and incols (i) work

Use  I="sequence" and i="sequence_comma".

* Ensure triangulate.delaunay_triples output_type is valid

Must be either one of numpy, pandas or file

* Autocorrect output_type to 'file' if outfile parameter is set
* Allow only str or None inputs to outgrid parameter

Xref GenericMappingTools#1807

* Use gmt get GMT_TRIANGULATE to check whether Watson or Shewchuk is used
* State that Shewchuk is the default triangulation algorithm

As per GenericMappingTools/gmt#6438

* Actually document the output_type parameter for delaunay_triples

Co-authored-by: Will Schlitzer <schlitzer90@gmail.com>
Co-authored-by: Meghan Jones <meghanj@alum.mit.edu>
Co-authored-by: Dongdong Tian <seisman.info@gmail.com>

doc/api/index.rst

@@ -124,6 +124,9 @@ Operations on tabular data
     sphdistance
     sphinterpolate
     surface
+    triangulate
+    triangulate.regular_grid
+    triangulate.delaunay_triples
     xyz2grd
 
 Operations on raster data

pygmt/__init__.py

@@ -56,6 +56,7 @@
     sphdistance,
     sphinterpolate,
     surface,
+    triangulate,
     which,
     x2sys_cross,
     x2sys_init,

pygmt/src/__init__.py

@@ -47,6 +47,7 @@
 from pygmt.src.subplot import set_panel, subplot
 from pygmt.src.surface import surface
 from pygmt.src.text import text_ as text  # "text" is an argument within "text_"
+from pygmt.src.triangulate import triangulate
 from pygmt.src.velo import velo
 from pygmt.src.which import which
 from pygmt.src.wiggle import wiggle