msgpack-rpc: Accept method names in requests
msgpack-rpc: Always use arrays when sending events or calls

This is required by the msgpack-RPC specification. Also, the
send_call/send_event functions were refactored to accept a variable number of
arguments
Fix environment variable for triggering embedded tests

NVIM should be used for all technical identifiers and this was changed in
the python-client
Merge PR #1121 'Full compliance with msgpack-RPC'