snapshot engine removed. it's tests and documentation removed as well.
(the engine can reincarnate on untrusted side later)
minor cleaning of the code
#264
#272 fixed. return code for invalid offset changed to conform pread()
channels tests updated. new case for #272 added. tests updated for
the new return codes in case of invalid offsets
zerovm version updated
return 4 if signal was received from the untrusted side and 25
if signal received from trusted code. a new document describing
zerovm return codes added
minor fix
minor change in the zerovm static linking script. bugfix in signal code
Merge pull request #278 from bortoq/devel

these are the last changes and fixes to zerovm version 2 code:

    snapshot removed
    bugfixes
    code cleaning
    tests updated