#13 support wider range of frame rates

[Lloyd Lim]

From Hank Magnuski (hankm@NCast.com):

"In the MASH code the variable "fps" is treated as an
"int" everywhere, and ordinarily this would not be a
problem for a typical video device.

However, we are constructing high resolution JPEG
digitizing devices for which the natural frame rate may
be measured in tens-of-seconds or even minutes, and fps
values below 1 are not treated well at all by MASH.

Also, it's hard to express a frame rate of 29.97 frames
per second as an int.

I would suggest the code be changed to treat fps(),
fps_, etc. as a "double" wherever it is found."