- Implemented 'oled_echo', a simple command line tool to display a string on the OLED.

- Experimental fast writes to the device (it doesn't work).
This is enabled with the SLOW_WRITE flag.  The result is lots of shear on screen.
Without access to the FR signal pin or read access to the status register, it doesn't
look promising.

- Fixed some typos.

- Instance global variables made static.

- All trailing spaces removed, and indentation cleaned up overall.

- Removed 'test' from oled_ctrl.c since the 0xe4 opcode is totally undocumented.
A consequence of that is all the send... methods are now private.

- Fixed compiler warnings; Implemented getOledDisplayName().