This provides a method to add symbols that represent footprints on the
board that do not have an associate component such as mounting holes,
fiducials, logos, etc that should be excluded from the bill of materials.
It also prevents those footprints from being removed from the board
accidentally when updating the board from the schematic.
ADDED: Support to exclude schematic symbols from bill of materials
export.
Please note that the symbol cache is not embedded in the schematic file
to allow for round robin testing with the existing file format. Once
the parser round robin testing is complete, the symbol cache will be
embedded in the schematic file.
This implements all existing symbol library object support and the ability
to save and load symbol library files between file formats for round robin
testing.
Seth Hillbrand
Jeff Young
Wayne Stambaugh