[Csnd-dev] fix for arbitrary number of pfields (PR #1764)

Hi all. Some weeks ago I opened a PR 
(https://github.com/csound/csound/pull/1764) to fix missing support for 
score events with an arbitrary number of pfields. This was particularly 
missing at the API level but also on certain opcodes. Without this fix 
score events are limited to ~1900 pfields, any event or API call with a 
larger amount results in csound crushing without any helpful error 
message. It would be great if it can be merged so that at least people 
building from source can use it.

On a side note there is some unnecessary copying on the process of 
handing over score messages with extra memory. For csound 7 there could 
be a way to signal insert_score_event_at_sample that it can own the 
memory passed.

thanks,
Eduardo