Be more consistent about log levels

LOG_ERROR should be used in places where though recoverable (or at least
something that can be handled safely), was unexpected, and may affect
the user/application.

LOG_WARNING should be used in places where it's not entirely unexpected,
is recoverable, and doesn't really affect the user/application.
Be just a bit more consistent.

See, it can sometimes be a bit confusing.  These functions should
definitely not fail under normal circumstances, and these errors may
affect the user and/or application in some way.
Fix a warning and an error

Happened because I compiled on windows and it only compiled
windows-specific code.
CoreAudio: Detect default device change

If the default device changes, set the reconnect interval to 200
milliseconds so it pretty much immediately tries to reinitialize the
audio with the newly selected default device.  Otherwise, use 2000
millisecond intervals, and assume disconnection.

Also, reduced FFmpeg logging to just regular FFmpeg information rather
than everything FFmpeg logs.
Give cf_parser functions better naming
Simplify and extend callback/signalling system

- Signals and dynamic callbacks now require declarations to be made
  before being used.  What this does is allows us to get information
  about the functions dynamically which can be relayed to the user and
  plugins for future extended usage (this should have big implications
  later for scripting in particular, hopefully).

- Reduced the number of types calldata uses from "everything I could
  think of" to simply integer, float, bool, pointer/object, string.
  Integer data is now stored as long long.  Floats are now stored as
  doubles (check em).

- Use a more consistent naming scheme for lexer error/warning macros.

- Fixed a rather nasty bug where switching to an existing scene would
  cause it to increment sourceSceneRefs, which would mean that it would
  never end up never properly removing the source when the user clicks
  removed (stayed in limbo, obs_source_remove never got called)