Implemented writing XML files with most profiles

This is currently missing support for a few fields and
is completely untested.

README.md

@@ -15,9 +15,9 @@ See the [Factur-X website (French)](https://www.factur-x.org/) or
 [FeRD website (German)](https://www.ferd-net.de/) for more information.
 
 Currently, this library supports writing XML files according Factur-X Version
-1.0.06 (aka ZUGFeRD 2.2) in the EN 16931 (Comfort) profile. Generally in scope
-of this library, but currently not supported are:
+1.0.06 (aka ZUGFeRD 2.2) in the profiles up to EN 16931 (Comfort). Generally
+in scope of this library, but currently not supported are:
 
-* Other profiles (Minimum, Basic, Basic WL, Extended, XRechnung).
-* Reading Factur-X files.
+* Extended and XRechnung profiles.
+* Reading Factur-X files (XML or PDF).
 * Embedding the XML in PDF files.

src/facturx/const.py

@@ -0,0 +1,18 @@
+"""
+XML Utilities for PyFactur-X
+"""
+
+URN_MINIMUM_PROFILE = "urn:factur-x.eu:1p0:minimum"
+URN_BASIC_WL_PROFILE = "urn:factur-x.eu:1p0:basicwl"
+URN_BASIC_PROFILE = (
+    "urn:cen.eu:en16931:2017#compliant#urn:factur-x.eu:1p0:basic"
+)
+URN_EN16931_PROFILE = "urn:cen.eu:en16931:2017"
+URN_EXTENDED_PROFILE = (
+    "urn:cen.eu:en16931:2017#conformant#urn:factur-x.eu:1p0:extended"
+)
+URN_XRECHNUNG_PROFILE = "urn:cen.eu:en16931:2017#compliant#urn:xoev-de:kosit:standard:xrechnung_2.1"  # noqa: E501
+
+NS_CII = "urn:un:unece:uncefact:data:standard:CrossIndustryInvoice:100"
+NS_RAM = "urn:un:unece:uncefact:data:standard:ReusableAggregateBusinessInformationEntity:100"  # noqa: E501
+NS_UDT = "urn:un:unece:uncefact:data:standard:UnqualifiedDataType:100"

src/facturx/countries.py

@@ -0,0 +1,6 @@
+import re
+
+
+def validate_iso_3166_1_alpha_2(code: str) -> bool:
+    """Validate an ISO 3166-1 country code in ALPHA-2 format."""
+    return re.match(r"^[A-Z]{2}$", code) is not None