add 4 function to read shp file with Z value

[wemamawe]

dear sir: i very thanks that you write this to read shape file, it help me a lot. when i use this to read 3D(x,y,z) shape file, it just return two dimension x and y, so i read you raw code carefully, and then i write some code to read Z value based on yours. recently i find some person get in to the same trouble like me, so i want to upload my code, and share to them. I hope you can accept my code, thanks again.

your follower, wema

[m-schuetz]

Should typenames in shp/polylinez.js be "LineString" or "LineStringZ" ?

[wemamawe]

i should explain this , there are many types in shape file like las format, so as the definition of ESRI, the type name should be LineStringZ, but for using easier, I set the type name as LineString.

[rowanwins]

Just a quick comment on this PR.

The GeoJSON spec does not have seperate types for Point and PointZ (and the same for other geoemtry types). If this lib is attempting to align to the geojson spec then bits like this would need some tweaking.

Cheers