Document security expectations
Currently I am not sure the Kaitai-generated code won't cause any security issues, so as a first step we should create a warning about this.

I have some ideas:
 - an attacker can create a specifically crafted .ksy file which can execute more privileged commands than the user would expect
   - more concrete example: if we'll support direct WebIDE links to user created ksys, that ksy may call an opaque class called Function which actually calls Javascript's Function and executes the argument (this probably won't work as it would expect string), or use some built-in property eg. `constructor` to access security-critical property (eg. `"".constructor.constructor("alert(1)")`).
 - an attacker can cause buffer-overflow or Denial of Service attacks by supplying specifically crafted payload to our generated parser
   - this may happen by causing integer overflow in expression and then abusing some parsing logic
   - or allocating too big buffer which makes a server which uses Kaitai non-responsive in the long run (something like this: https://github.com/weidai11/cryptopp/issues/346)

Currently I did not evaluate whether we are susceptible problems listed above or not. That's why we should warn our users that we are not recommending executing code generated from untrusted ksys and untrusted inputs as a determined attacker may can cause harm.

Of course later we should evaluate whether these issues can arise or not to our best knowledge and solve them if we can.