RT90 to WGS84 coordinate transformation

Conversion of geographical coordinates from the RT90 format (Sweden) to WGS84 (e.g Google Earth)

Different countries in the world use different geographical coordinates. In Sweden coordinates are often expressed in a format known as RT90. Even if this format can be practical, it is not a worldwide standard.

This function converts RT90 coordinates to the WGS84 format, which is more widely used. For instance, Google Earth uses WGS84.

The algorithm used in this function is adapted from https://gist.github.com/moonhouse/2602783