zencode execution is now reentrant, running ZEN:begin() again clears
the HEAP and AST and processes a new STACK within the same running
Zenroom VM instance.

new generic class for basic homomorphic arithmetics as used in COCONUT
petitions

fixes handling of zero values, adds tests for basic operations with
BIG and ints and cleans up the code

also small fix to petition calculation

simple method returning ratio,max and bits according to Shannon's way
to measure information entropy, useful for benchmarks and to measure
the quality of random in Zenroom

This correctly outputs raw byte data instead of passing by string()
conversion via print which eats away chunks. Useful for rngtest and
other programs expecting raw bytes from stdin

added printerr function to plain print to stderr
added 'rule output AST' for zencode
AST output to stderr surrounded by #+AST_BEGIN and #+AST_END

avoid reporting 'and' and list parent section
optimised use of parse_prefix

move seccomp extern conf flag out of ifdef

general improvements to how determinism is handled

added a function to publish C buffers in zenroom octets

standalone AST generation by ZEN:parse()
some cleanups in function scoping

correct use of statemachine and start to modularization of
parse/AST/execution