README* refactoring

This is an attempt to bring the README files in line with the current
status of the OpenOCD development.

- remove some obsolete information and duplicated instructions
- reword some statements
- restructure in a way more appealing to a regular user
- add a supported hardware list to allow a potential user to determine
  if his/her usecase is covered by a freetext keyword search through
  the document
- Add OSX notes (courtesy GrizzlyAdams and inca)

Since most ftdi-based adapters are now covered by the ftdi driver, I
think it's ok to remove some of the libftdi/ftd2xx instructions, the
few users who still need them should refer to upstream docs instead.

I'm not sure if README.Windows should come with the DOS line endings,
but i'd expect many windows users to use their silly notepad to view
it, and notepad ignores LF apparently. (Decided to use LF anyway.)

I understand discussing and reviewing such a massive README change is
a somewhat demanding task but I feel it's a necessity to move forward
maintaining proper documentation.

Change-Id: Idfde3014c72dd5c32ad292ee1ab205322e51a138
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1503


Tested-by: jenkins
Reviewed-by: Xiaofan <xiaofanc@gmail.com>