Fix #90. Fix Wkt scope problem and adds arcgis working samples.

[cancastilho]

To solve 'multiple define errors' when using this library with arcgis, Wkt variable must be set as global scope.

This pull request adds working samples for arcgis javascript api version 3.x and 4.x. To see them working, you should start a http-server from the project root path and open the url as following:

http://localhost:8080/doc/arcgis3.html

or

http://localhost:8080/doc/arcgis4.html

I recommend deleting the old arcgis.html sample, since it's not working.

[arthur-e]

This is great! Thanks.

[arthur-e]

Just want to add a link indicating this fixes #90.

[arthur-e]

This does indeed fix the demos in the doc/ folder, if someone sets up a local HTTP server. However, I am struggling with how to fix the demos on the gh-pages branch. These are the ones that people actually see (i.e., on the public web) and are referenced in #90 and #152.