Backport perf, crash and exception handling fixes

The following commits are backported:

e41ccd4e2de6deb03e277fa9d6baff685ab31689 - performance fix
2a08925896872c345e2948778eab01e9853c22cb - performance fix follow-up
978d89f5e3cf238a0e42303acc9493993ede9c98 - make functions gc-able
c1695d8bad09fc61922ec91101736debb2d165db - add napi_fatal_exception()
9e226475e8e28b8664643d6644503ccd06bceb9a - exception handling fix
1a5a19d6d475578eec355a8b3079b4a96fc77489 - crash fix

PR-URL: #295
Reviewed-By: Nicola Del Gobbo <nicoladelgobbo@NickNaso.local>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

Author: Gabriel Schulhof