Totally reworked classes separation to respect packaging conventions.

Reworked FileConfiguration#addParsers method.
Renamed `it.fulminazzo.yamlparser.configurations` package to `it.fulminazzo.yamlparser.configuration`.
Made FileConfiguration and ConfigurationSection final.

src/main/java/it/fulminazzo/yamlparser/configuration/ConfigurationSection.java

@@ -8,7 +8,7 @@
  * Represents a YAML Section.
  */
 @Getter
-public class ConfigurationSection extends SimpleConfiguration {
+public final class ConfigurationSection extends SimpleConfiguration {
     private final IConfiguration parent;
 
     public ConfigurationSection(IConfiguration parent, String name) {

src/main/java/it/fulminazzo/yamlparser/configuration/FileConfiguration.java

@@ -20,7 +20,7 @@
 /**
  * Represents a YAML File configuration.
  */
-public class FileConfiguration extends SimpleConfiguration {
+public final class FileConfiguration extends SimpleConfiguration {
     private final static LinkedList<YAMLParser<?>> parsers = new LinkedList<>();
     private final @Nullable File file;