Add --game_data flag for setting a user-defined PATH_DATA

This should be handy for engine developers. Previously, there were two
methods for testing code in this repo against the contents of the
flare-game repo:

* Copy the executable to the flare-game repo directory.
* Install flare-game system-wide.

Now, those can be avoided by using something like this:

`./flare --game_data ../flare-game/`

This commit also moves commandline argument parsing outside of the
mainLoop() and into the beginning of main(). This will be necessary if
we want to define `engine_folder` via arguments in the future.
Support '=' in command line arguments

This commit abstracts argument parsing a bit. Arguments that need
values, such as `game_data` now use '=' to assign those values.
Also, arguments are now always assumed to start with '--'.
Reload footsteps sound effect when untransforming
Merge pull request #355 from dorkster/transform

Reload footsteps sound effect when untransforming
Merge pull request #353 from dorkster/bugfixes

Add --game_data flag for setting a user-defined PATH_DATA
Initial version of SoundManager for a more central handling of
sound playback All loadSfx() and playSfx() has been replaced
though the codebase to use the new SoundManager.
Fix indentation.
Added a VirtualChannel for syncronous playback of specific
sounds, such as dialogs were the current vox playback should
stop before next vox should play. This moves local sound logics
such in NPC for quest dialogs vox.

Make NPC use the new VirtualChannel playback and remove old
local logic for stopping previous vocal before playing next.
Remove the use of fixed array or sound references and make
items to specify the audio file instead of the hardcoded list
of reference names such as "maille" etc..

Fixes #342
Merge pull request #356 from hean01/soundmanager

Minimal approach for a SoundManager
Make the vendor inventort sound always play even if
trader have greetingvocals.