FFI class improvements (fixes #221)

[uuf6429]

Changes (all backward compatible!):

• a few minor improvements to comments
• fixes loadLibrary return type (it can now return null, which is then handled by caller)
• adds a new library path for osx/brew (see also link in comment)
• tiny simplification to cpp script to avoid HEREDOC interpolation
• changed all HEREDOCs to NOWDOCs (among other things, doesn't require escaping dollar signs etc)
• changed all NOWDOC terminators to "CPP" - participating IDEs can highlight the code in those strings properly based on that

While the change in return type should fix the error from #221, hopefully adding the extra search path also fix the root cause behind it too.

[jcupitt]

This is great, thank you @uuf6429!

I'll try to take a look today.

[uuf6429]

@jcupitt I've improved the code style a bit more in a separate branch: 14f9c79 (consistent NOWDOC indentation; unambiguous condition)
What do you think, is it too much? If you're ok with it, I can cherry-pick it into this PR (if not we can leave it out).

[jcupitt]

Sorry for the delay, I've been working on other stuff.

Let's merge this and maybe have another PR for the code style changes you suggested. I left a comment on that branch.