Add validation for Guatemala TIN number

[unho]

• https://en.wikipedia.org/wiki/VAT_identification_number
• Online NIT search: https://portal.sat.gob.gt/portal/consulta-cui-nit/
• Details on the structure: https://portal.sat.gob.gt/portal/descarga/6524/factura-electronica-fel/25542/fel-reglas-y-validaciones.pdf (page 58)

Algorithm:

• http://ficoaex.blogspot.com/2012/10/como-se-valida-un-nit.html
• https://opcontable.weebly.com/opc-blog/digito-verificador

Implementations:

• JavaScript: https://gist.github.com/rodrigopolo/0807e96a5331eb17e819f485d9a3c891
• Other JavaScript (with explanation): http://mariobatres7.blogspot.com/2008/02/validar-el-nit-con-modulo-11.html
• Another JavaScript: https://jsfiddle.net/miguelerm/j54bt1yk/
• Yet another JavaScript: http://curiosidades-de-juancho.blogspot.com/2012/07/funcion-para-validar-nit-guatemala.html

Examples:

• http://anam.org.gt/LAIP/anam/wp-content/uploads/2018/01/ANAM-22-2017-12-COMPRAS-DIRECTAS.pdf
• https://vicepresidencia.gob.gt/sites/default/files/Compras%20Directas%20Marzo%202018.pdf
• http://www.minfin.gob.gt/images/laip_mfp/docs/item14_dsa.pdf
• http://www.minex.gob.gt/MDAA/DATA/MDAA/20101006160918560Aspecto%2022_Compras%20directas%20de%20Septiembre%202010.pdf
• http://www.inguat.gob.gt/uip/images/PDF/articulo10/22_compras/COMPRAS_DIRECTAS_NOVIEMBRE_2017.pdf
• https://www.saas.gob.gt/informacion-publica/decreto-57-2008/category/479-22-compras-directas-2017?download=1675:07-informacion-de-compras-directas-julio
• http://fopavi.gob.gt/Portal_Libre_Acceso/files/10%20-%2017%20-%20Empresas%20precalificadas%20para%20la%20ejecucion%20de%20obras%20publicas%202017.pdf
• https://www.fontierras.gob.gt/ip/21Fideicomisos/COMPRAS_JULIO.pdf
• http://www.civ.gob.gt/c/document_library/get_file?folderId=10731&name=DLFE-7015.pdf
• http://uip.mingob.gob.gt/archivouip2009_2017/images/documentos/direccion_superior/numeral22/DIRECCIONSUP_DISAF_NUMERAL_22_COMPRAS_DIRECTAS_DICIEMBRE_2013.pdf
• http://www.munisanbenito.laip.gt/index.php/files/330/22-COMPRAS-DIRECTAS/id:e6bAINJ_TsAAAAAAAAAA6A/2.-COMPRAS-DIRECTAS-ANO-2017.pdf
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