Using PRNG to generate an IV is not a good idea

[fulopm]

As far as I can see, the IVMode class (https://github.com/soywiz/haxe-crypto/blob/master/src/com/hurlant/crypto/symmetric/mode/IVMode.hx) uses a PRNG (which is seeded from the system clock) to generate the initialization vector.
I recommend you guys to use the SecureRandom class, and manually generate an IV instead of the default mode.

[soywiz]

Please, create a PR for this and I will happily merge it :)
I don't have too much time to invest in this, but I I can merge stuff and make releases.