Fix boundary definition bug in ArcGIS and Grid headers

[atdyer]

The point (min_x, min_y) is the southwest corner of the bounding box of the input dataset as well as the center of the bottom left cell in the grid, and the point (max_x, max_y) is the northeast corner of the bounding box of the input dataset.

The ArcGIS format allows the coordinates of the origin to be defined by either the center or lower left corner of the lower left cell. I've fixed the values printed to be consistent with the lower left corner.

The GRASS Grid format calls for the N, S, E, W boundaries to describe the outer edges of the region. Printed values now represent these edges instead of the bounding box of the input dataset.

Related to bugs #6 and #7

[gadomski]

@atdyer code looks ok to me. One nit before I merge: any way you could add a unit test or two? I've provided an example of testing the asc header here — you could just include that test, and maybe add a corresponding one for the grid format as well?

Also, curious if you've checked the geotiff headers to see if the problem exists there as well?

[atdyer]

@gadomski I've included your asc header unit test as well as added a single grid format test. Working on an additional (slightly larger) point cloud for testing purposes.

It looks like the problem does exist in the geotiff files...the results appear different when opened in GRASS GIS. Am currently researching how coordinate systems are defined in gdal/geotiff.

[gadomski]

Awesome, looks great. I'm going to merge, and I've opened #18 for the geotiff issue.

Thanks @atdyer.