Eeschema: implement s-expression schematic file format parser.

Please round robin test the schematic parser so we can get this merged into the master branch. You will have to save the legacy schematic with master because there was sorting recently added to the legacy formatter so ordering of 5.1 files will be completely different.

There are a few caveats. *Eeschema has to run in the stand alone mode because the project manager still defaults to loading the legacy format. *Hierarchal sheets will have to be "Save As..." individually to the new file format and the sheet file name extension changed from .lib to .kicad_sch.

If all looks good, I will merge this and send out a request for testing to the dev mailing list to get some additional testing. I'm hoping to finish up the code to transition to new file format in early April and make the new file formats the default by the end of April.