[Nitro: Code was cleaned and several bugs at writing process were fixed]

* NumericExtensions.cs: Fixed bugs.

* Format.cs: Added new write method.

* DataStream.cs: Fixed bugs
Added write to file method

* DataWriter.cs: Fixed bug with endiannes (it was doing the inverse)
Added write fixed size string method

* XmlExportable.cs: Since it inherit from Format no need for
  TypeExtensionPoint method.

* Program.cs: Added new NDS ROM test.

* Banner.cs: Cleaned code.
Fixed bug writing game titles.

* Fat.cs: Cleaned code.
Fixed bug.

* Rom.cs:
* RomHeader.cs:
* FileSystem.cs:
* OverlayFolder.cs: Cleaned code.

* Fnt.cs: Cleaned code.
FntTable must a structure since its data can not be changed
  (inmutable)

* OverlayFile.cs: Cleaned code.
Fixed bug: it was setting no name.