rtc: a pedestrian real-time clock figure

- creates a real-time clock (using a timer object), which runs smoothly in the background while the user continues with her daily ML chores.
- all aspecects of the display (geometry) are user-definable.
- the clock can be stopped and restarted (toggled)

help rtc
RTC a pedestrian Real-Time Clock
- start
[par] = rtc
- start with previously saved geometry
[par] = rtc('i',par);
- stop
[par] = rtc % toggle
rtc s % delete clock
- display/retrieve current geometry parameters
rtc d
par=rtc('d');
- update geometry
[par] = rtc('u',par);
- show parameter description
rtc h
- save current geometry in mat-file <fn> var <v>
[par] = rtc('S',fn);
- reload geometry from mat-file <fn> var <v>
[par] = rtc('L',fn);

EXAMPLE
rtc; % start real-time clock
par=rtc('d'); % get current geometry
par.F.w=[[300 300]... % change figure position
[400 400]];
par.F.col=[.5 .75 .75]; % change figure bg color
par.H.mark='diamond'; % change HR marker
par.H.fcol=[1 1 0]; % change HR color
par.M.fcol=[.4 .5 .75]; % change MIN color
par.M.size=3; % change MIN size
rtc('u',par); % apply
pause(5); % run
rtc; % stop
pause(5); % wait
rtc; % cont