Add U8glib as a dependency to platformio.ini for those who use PlatformIO; this makes compiling even easier as u8glib will be downloaded and included automatically.
Also added the new .pio-related directory to .gitignore, and a few ignores for those who use cmake.
.gitignore: Add *~, *.orig, *.rej, move to root directory
Move the .gitignore out of the Marlin subdirectory so it applies to
the whole tree, and add some missing patterns.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>