Fix to pcl::io::load and pcl::io::save

[SergioRAgostinho]

The implementation of the template methods pcl::io::load and pcl::io::save was in pcl/io/src/file_io.cpp. Not only was this not conforming with pcl style guide, bit it also rendered the methods useless, since the compiler could not find the appropriate symbols.

I just moved the code around between files and edited the CMakeLists.txt and now everything should be ok.

Edit: I now noticed that the proper way to do this is to mimic what was done in pcd_io.h and pcd_io.hpp, but right now that creates a circular reference.

[SergioRAgostinho]

The problem:

pcl/io/file_io.h is divided in 4 sections: the pcl::FileReader class, the pcl::FileWriter class, a bunch of string utility methods and finally a section with pcl::io::save and pcl::io:load which write and read from a file (PCD, PLY, IFS, etc...) based on the extension provided in the file name.

pcl/io/pcd_io.h, pcl/io/ply_io.h, etc..., depend on pcl::FileReader and pcl::FileWriter from pcl/io/file_io.h.

The methods pcl::io::save and pcl::io:load depend on pcl/io/pcd_io.h, pcl/io/ply_io.h. This creates a circular reference with the template versions of pcl::io::save and pcl::io:load which need to be moved to a header file and included from file_io.h

Proposed solution:

Move methods pcl::io::save and pcl::io:load to a new file. I just need a good name for it, other than file_io. Some ideas: all_io.h, xxx_io.h, auto_io.h. I'm inclined towards the last one.