Es VAT checksum validation with all AEAT rules

[KirtashW17]

Applies more rules to SPAIN VAT Number validation:

• CIF: If first digit is in [ABCDEFG], check-digit can be both a letter or a number.
• CIF: If first digit is in [HJUV], check-digit MUST be a number.
• CIF: If first digit is in [NPQRSW], check-digit MUST be a letter.
• Adds rules for special NIF's [KLM]: First two digits must be between 01 and 56 (inclusive).

Based on official AEAT VAT validation Library written in Java:

• https://ws024.juntadeandalucia.es/maven/repository/internal/com/aeat/valida/valnif/2.0.1/
• http://www.migoia.com/website/articulos/NIF.html

I also did some JJUnit tests to confirm this behaviours of the official library:

• ValNifTest.zip