VizEquiMap improvements

(NOTE: This issue is moved from s2dv about s2dv::PlotEquiMap)

Here are a few things that can be improved in PlotEquiMap().

• (1) Follow the development in s2dv!94 (merged), it's better to calculate params xlabels and ylabels in the function (s2dv!94 (comment 170834)). If xlabels = NULL, the labels can still be correct (see the right figure in s2dv!94 (comment 169024)). The parameters should still be open for customizing labels.

• (2) discrete color bar: If the color bar is for categorical data, the name of each category should be placed in the center of each color. (In new package)

• (3) Two dots: Allow dots to be a list of arrays and plotted by different shapes.

• (4) dots dimensions are not checked and reordered as data. The longitude and latitude dimensions of the input should be flexible.

• (5) Add crop argument to crop the desired region. So the input data lat and lon don't need to be subset beforehand

• (6) first_lon: users can define the longitude border and the function adjusts the data accordingly. For example, the data is [0, 360] but first_lon = 330, then the function needs to rearrange the data to [330:360, 0:330] then do the plotting.

• (7) Deal with value Inf: Inf is not NA and it should belong to the triangle at the ends of color bar. We can say Inf <- max + 1 and -Inf <- min - 1 in the code.

• (8) Add param closedevice like PloyLayout() has.

• (9) Fixed coordinate s2dv#43

• (10) caption s2dv#98 (closed)

• (11) mask s2dv#98 (closed)

• (12) vertical colorbar

• (13) select the color of the dots

• (14) hatching #13 (closed)

• (15) fix map contours not reaching left edge of plot #23 (closed) !32 (merged)