Fixed broken links

- Updated CONTRIBUTING.md
- Updated documentation

CONTRIBUTING.md

@@ -6,8 +6,8 @@ This document will get you on the right track to help improve eInvoicing.
 Use the following sites to get more information about the European electronic invoicing specification:
 
 - [EU e-Invoicing core concepts](https://josemmo.github.io/einvoicing/getting-started/eu-einvoicing-concepts/)
-- [Compliance with the European standard on eInvoicing](https://ec.europa.eu/cefdigital/wiki/x/ggTvB)
-- [Obtaining a copy of the European standard on eInvoicing](https://ec.europa.eu/cefdigital/wiki/x/kgLvB)
+- [Compliance with the European standard on eInvoicing](https://ec.europa.eu/digital-building-blocks/sites/x/PoTXGw)
+- [Obtaining a copy of the European standard on eInvoicing](https://ec.europa.eu/digital-building-blocks/sites/x/a4TXGw)
 - [UBL Invoice fields](https://docs.peppol.eu/poacc/billing/3.0/syntax/ubl-invoice/tree/)
 - [CEF eInvoicing Validator](https://www.itb.ec.europa.eu/invoice/upload)
 

docs/getting-started/eu-einvoicing-concepts.md

@@ -3,7 +3,7 @@ Prior to using this library, there are some key concepts about European e-Invoic
 
 ## EN 16931
 The European e-Invoicing standard (EN 16931) describes the **semantic data model** and business rules of an electronic
-invoice. In other words, this document (specifically [part 1][1]) specificies **what an invoice is** (fields it must/can
+invoice. In other words, this document (specifically [part 1][1]) specifies **what an invoice is** (fields it must/can
 have) and the possible values those fields can contain.
 
 But that's it: it just gives an abstract definition of an invoice without getting into the technical structure (syntax).
@@ -41,5 +41,5 @@ international companies from both public and private sectors.
 
 [1]: https://ec.europa.eu/digital-building-blocks/wikis/display/DIGITAL/Navigating+the+eInvoicing+standard+documentation
 [2]: https://ec.europa.eu/digital-building-blocks/wikis/display/DIGITAL/Required+syntaxes
-[3]: https://ec.europa.eu/digital-building-blocks/wikis/display/EINVCOMMUNITY/Registry+of+CIUS+%28Core+Invoice+Usage+Specifications%29+and+Extensions
+[3]: https://ec.europa.eu/digital-building-blocks/sites/display/EINVCOMMUNITY/Registry+of+CIUS+%28Core+Invoice+Usage+Specifications%29+and+Extensions
 [4]: http://docs.peppol.eu/poacc/billing/3.0/

docs/getting-started/installation.md

@@ -1,6 +1,6 @@
 # Getting Started
 eInvoicing (short for "European Invoicing") is a free and open-source library written in PHP for creating and reading
-electronic invoices compliant with [EN 16931](https://ec.europa.eu/digital-building-blocks/wikis/x/boTXGw).
+electronic invoices compliant with [EN 16931](https://ec.europa.eu/digital-building-blocks/sites/x/HYPXGw).
 
 ## Requirements
 In order to install this library, your environment has to meet the following requirements:

docs/index.md

@@ -2,7 +2,7 @@
 
 eInvoicing is a PHP library for creating and reading electronic invoices according to the [eInvoicing Directive and European standard](https://ec.europa.eu/digital-building-blocks/wikis/display/DIGITAL/eInvoicing).
 
-It aims to be 100% compliant with [EN 16931](https://ec.europa.eu/digital-building-blocks/wikis/x/boTXGw) as well as with the most popular CIUS and extensions, such as [PEPPOL BIS](https://docs.peppol.eu/poacc/billing/3.0/bis/).
+It aims to be 100% compliant with [EN 16931](https://ec.europa.eu/digital-building-blocks/sites/x/HYPXGw) as well as with the most popular CIUS and extensions, such as [PEPPOL BIS](https://docs.peppol.eu/poacc/billing/3.0/bis/).
 
 [Get Started](getting-started/installation.md){: .md-button .md-button--primary }