Made love.keypressed() call LNVL.Advance().

This makes the love.keypressed() work in a more proper way and lets the user of LNVL recreate a custom love.keypressed() which will simply have to call LNVL.Advance() to advance through the scenes.
Initialized variables to gradually draw text.

Those were left uninitialized after merging. Some small changes were also done such as removing a useless assert in and removing a useless local variable, to make the code cleaner in short.
Added a dialogSpeed to the example.

This lets us experience the difference between the dialogSpeed of Eric and Jeff's.
Reinitialized the displaySpeed in LNVL.Advance.

This lets us modify the displaySpeed at our will without worrying about not having a default one.
Added a dialogSpeed element to each character.

This element determines the speed at which the dialog will be displayed when this character is talking.
Added a displaySpeed initialization in DrawText.

This lets us change the display speed at our will depending on the character. I also added a default value for this display speed to ensure we always have one.
Modified the call to LNVL.Graphics.DrawText.

Added a variable to modify the displaySpeed within LNVL.Graphics.DrawText.
Testing the display speed change too now.
Change of the display speed for each character.

Here, we're changing the display speed of a character depending on the scene's particular speed for this character. If none has been defined, we just use the default value for the character.
Added the speedTable to the scene object.

This speedTable lets us change each character's display speed for the current scene.
Merge commit 'b18e5bea4afae6f650618e7575d70e39902e732d'

* commit 'b18e5bea4afae6f650618e7575d70e39902e732d':
  Added the speedTable to the scene object.
  Change of the display speed for each character.
  Testing the display speed change too now.
  Modified the call to LNVL.Graphics.DrawText.
  Added a displaySpeed initialization in DrawText.
  Added a dialogSpeed element to each character.
  Reinitialized the displaySpeed in LNVL.Advance.
  Added a dialogSpeed to the example.
  Initialized variables to gradually draw text.
  Made love.keypressed() call LNVL.Advance().