* Add s-expression file parser object and keyword files.
* Fix minor issues with s-expression file formatting.
* Fix a minor bug the zone container fill state parsing in the legacy plugin.
* Move EDA_TEXT visibility definition to eda_text.h.
* Add minor BOARD_ITEM object improvements to support s-expression file
parser.
Other scaling factors (MILS_TO_IU_SCALING_FACTOR and DECIMILS_TO_IU_SCALING_FACTOR)
also defined only in convert_to_biu.h.
Allows different scaling value for Gerbview.
Needs more tests.
* Move board item object Format() functions into PCB_IO object.
* Change file format to use layer names instead of numbers.
* Change file extension to kicad_pcb.
* Move EDA_TEXT object into separate header and source file.
* Compile EDA_TEXT class separately for BOARD_ITEM and SCH_ITEM units.
* Compile PAGE_INFO class separately for BOARD_ITEM and SCH_ITEM units.
* Minor formatting tweaks to Pcbnew s-expression file.
* Move internal unit formatting functions into BOARD_ITEM and SCH_ITEM.
Wayne Stambaugh
jean-pierre charras