[types] add support for new telemetry types

Comming from the old 'messages' branch:
- support for char and 64 bytes
- support for fixed length arrays
[convert] support for ARCH_ALIGN_INT64
[messages] add char, fixed size array and int64 support to transports and gen_messages.ml
Merge pull request #589 from gautierhattenberger/pprz_type

[types] add support for new telemetry types