Added more structure methods and some quality of life changes

Overall cleaned up a lot of comments.

EasyGA:
- Code cleanup.

Population:
- Added sort_by_best_fitness
- Added parent/mating pool methods.
- Renamed some methods for consistency.

Chromosome:
- Added get_gene(index).

Parent Selection:
- Improved selection methods to use the ga.selection_probability so that the roulette selection actually works well.
- Added stochastic selection.

Survivor Selection:
- Added fill_in_random and fill_in_parents_then_random.

Crossover/Mutation:
- Cleaned up code.

src/structure/chromosome.py

@@ -24,9 +24,15 @@ class Chromosome:
 
 
     def remove_gene(self, index):
+        """Removes the gene at the given index"""
         del self.gene_list[index]
 
 
+    def get_gene(self, index):
+        """Returns the gene at the given index"""
+        return gene_list[index]
+
+
     def get_gene_list(self):
         return self.gene_list