Draft: Create first public API with libmuttum 1.0.0

To create a better usable public API, we create more objects.

I still want to improve this merge with:

• MuttumLetter:
  • Update from struct to GObject with grapheme and state public properties
  • Create a copy function (GObject style)
  • Create init function with useful default values (state)
  • Create a derived type MuttumAttemptLetter with known-grapheme property
  • Create a derived type MuttumAlphabetLetter with found-count property
• MuttumAttempt:
  • Create a copy function
  • Correctly free sub-objects
  • Add construct-only readable "n-letters" property
  • Improve foreach function signatures (GFunc is too generic)
• MuttumBoard:
  • Create a copy function
  • Correctly free sub-objects
  • Improve foreach function signatures (GFunc is too generic)
• MuttumAlphabet:
  • Creates this GObject like the MuttumAttempt (list of MuttumAlphabetLetter with all possible grapheme in current language)
  • Create a foreach function to go through all letters
  • Have a way to know the total number of letters
• MuttumEngine:
  • Use GObject properties to construct (n-attemps, min-word-size, max-word-size, dictionary) and to access read-only state (current-attempt-number)
  • Create MuttumDictionary and give it as parameter to MuttumEngine (this will allow to let client to configure the engine) + Remove dictionnary from MuttumEngine class members