json_escaped.[ch], param.[ch] and jsonrpc_errors.h move from lightningd/
to common/. Tests moved too.
We add a new 'common/json_tok.[ch]' for the common parameter parsing
routines which a plugin might want, taking them out of
lightningd/json.c (which now only contains the lightningd-specific
ones).
The rest is mainly fixing up includes.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>