Add an X Resource for the Cursor Blinking Interval?

[Bastien Dejean]

Hi,

At the moment, there's no available X resource for changing the cursor
blinking interval, although I found the relevant constant
in `feature.h`, I think it would be simpler to add an X resource.

I'd also like to change the *stay visible*, *become invisible*, *stay
invisible* and *become visible* intervals but I'm not sure if those
values are explicitly defined somewhere. 

Greetings,
-- 
 b.d
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