This renames the android target to android-arm|android-x86 and makes it
easy to add future targets, such as android-x86_64 or android-aarch64.

not cryptographically valid, just an example (WIP)

Add references to Coconut .pdf ( https://arxiv.org/pdf/1802.07344.pdf ) and to variable names, used in the paper

Tested with cmake-3.13.2.

may refine a bit the interpreter however that's it

WIP: this is not safe enougn and needs validation (see ECP import)

work in progress

need to check all other lerror calls

two new namespaces for the crypto schemes

works with multiple authorities, but without threshold

completed aes-gcm encryption usecase and wip on certificate
better wrapping of ZEN.data, keyring and ZEN.assert

modularization, better error reporting and data handling

spotted inconsistency across conversions octet/string/BIG
isolated the problem in a new section of octet tests
needs more work to make serialize fully deterministic