minor code cleaning. fixed minor warnings in debug mode.

inches and mm, the industry is crazy enough to force us with mixed
design. For example I routinely use imperial units for track size and
clearance, but drilling is strictly a metric issue...

So I added a little parser to recognize a suffix specification in the
unit text boxes... so you can put in things like:
1in (1 inch)
1" (idem)
25th (25 thou)
25mi (25 mils, the same)
6mm (6 mm, obviously)

The rules are: spaces between the number and the unit are accepted, only
the first two letters are significant.

As a bonus, it also recognize the period (.) as a decimal point
substituting it with the correct locale character (there was a wishlist
for it, IIRC). Most useful for number pad fans :D 

Added an experimental tool to create logos from .bmp bitmaps. Added Potrace library to convert bitmaps to polygons

* Fix a minor problem with wxFileDialog to open a file that no longer
  exists in PCBNew.
* Make GerbView open file behavior the same as PCBNew.
* Remove redundant PCB file wild card definition.
* Add open file refactor task to the todo list.
* Fix some minor code formatting issues.

fixed others very minor bugs.

fixed very minor bugs.

* Some bugs fixed
* Starting enhancements in Libedit: menubar and commands to "plot" current component in PNG or SVF file (SVG file not fully working, must be refined)

* Make USE_WX_ZOOM clipping routine actually clip rather than just test
  if line needs drawn.
* Clean up as many USE_WX_ZOOM #ifdefs as possible.
* Minor coordinate rounding improvements.
* Minor scrolling and panning improvements.
* Remove unused KicadGraphicContext object code.

All: added in popup menus hotkeys info for zoom commands

* Implement code to allow wxDC to handle coordinate conversions between
  device and drawing units.
* Add build settings to enable wxGCDC for wxGraphicsContext testing.
* Remove wxAUI conditional build cruft as it is now required to build
  Kicad.
* Fix scroll increment size regression to prevent jumping around the
  zoom center position.
* Add find GDI+ cmake module for building on WXMSW when wxGraphicsContext
  is enabled.

Added sample gerber files for test (gerbview has problem with 2 files)

Added sample gerber files for test (gerbview has problem with 2 files)

removed global variables and a lot of redundancies

hide/show rastnest in pcbnew is currently not working, will be fixed soon

    * in variable names, change non existent word Hight to High
    * Remove redundant tool in left toolbar (option toolbar)
      (this option is now in layers manager)
    * Show layers in horizontal combo box in same order as in layer manager.
++all:
    minor code cleaning.

* Remove redundant background redrawing RedrawActiveWindow.
* Remove redundant managed cursor callback in RedrawActiveWindow.
* Use refresh to redraw instead of directly calling RedrawActiveWindow.
* Remove unused SetDrawBgColor for drawframe.cpp.
* Fix compiler warning in cvpcb/cvframe.cpp.
* Fix menu spelling and syntax errors in pcbnew.
* Rename Trace_Curseur to DrawCursor in common/drawpanel.cpp.

Code cleaning.
Patch for 3D problem with macOSX

Added patch for macOSX
turn on fast algo for draw grid (should work now)

* Fix debug asserts when passing NULL pointers to wxAuiPaneInfo.
* Fix Kicad main window sash sizer bug when using wxAui.
* Remove specctra_test from Visual Studio builds to prevent build errors.
* Add WIN32 to layer widget test so it will build properly on Visual Studio.
* Fixed compiler conversion warnings in PCBNew.
* Fixed worksheet print scaling in PCBNew.
* Minor code renaming.