Adds infinite maps docs

[ketanhwr]

No description provided.

[bjorn]

Please wrap the lines, say to 78 characters.

The documentation for <chunk> is too short. It should mention "Can contain: tile", like other elements are documenting their possible child elements. Also, the element should be mentioned at <data>, at least as part of the "Can contain" list of elements.

Somewhere, probably as part of the <chunk> documentation, it should be mentioned that the contents is the same as for the <data> element, except that it only stores the data for the area specified with the attributes and that no <chunk> element can be nested in a <chunk>.