Underscored functions are allowed with passed via only
Improve how exceptions are handled in general

* raise expects an explicit stacktrace in order to re-raise
* the Exception module now holds function for both stacktrace
  manipulation and interface with erlang exceptions
* exceptions have their default functions with doc set to false
Update CHANGELOG
Keep \377 and 0377 as the octal syntax, closes #737
Discard spurious cons list from stacktrace
Rename BOOTSTRAP to __BOOT__
Fix test since we return a four item tuple in the stacktrace
Do not rely on the third arg of catch clauses

This is an undocumented Erlang feature and it
must not be part of Elixir public API.
Propagate configs from ParallelCompiler in ParallelRequire