options: alternative way to specify color options

Try to make it more intuitive by not requiring hex values. The new way
uses float values in the range 0.0-1.0, separated by '/' (':' was
suggested, but that wouldn't allow color options in sub-options).

Example: --osd-color=1.0/0.0/0.0/0.75

Using the range 0.0-1.0 has the advantage that it could be easily
extended to colors beyond 8 bit.

Details see manpage.

Suggestions for alternative syntax or value ranges are welcome, but be
quick with it.
quvi: disable subtitle fetching by default

This is slow and unreliable, basically unusable.