MIL-001 Repository foundation: baseline documents, project configuration, CI and Doxyfile

Business Case, Stakeholder Analysis, Project Plan and MIL-001 accepted
with review records; ADR-0001 and ADR-0002; pyproject.toml, .gitignore,
package skeleton, Doxyfile and Gitea CI workflow.

Task: MIL-001#1
Task: MIL-001#2
Task: MIL-001#3
Task: MIL-001#4
Task: MIL-001#5
Task: MIL-001#6

src/nato_phonetic_alphabet/constants.py

@@ -0,0 +1,35 @@
+"""@brief Constants of the NATO alphabet tool.
+
+Every literal that the program, its messages or its data loading depend on is
+defined here once.
+"""
+
+## @brief Name of the package that holds the data file.
+DATA_PACKAGE: str = "nato_phonetic_alphabet"
+
+## @brief Folder inside the package that holds the data file.
+DATA_DIRECTORY: str = "data"
+
+## @brief Name of the comma-separated values file with the NATO alphabet.
+DATA_FILE_NAME: str = "nato_phonetic_alphabet.csv"
+
+## @brief Header of the column with the letter in the data file.
+LETTER_COLUMN: str = "letter"
+
+## @brief Header of the column with the code word in the data file.
+CODE_COLUMN: str = "code"
+
+## @brief Text shown when the program asks for a word.
+PROMPT_TEXT: str = "Enter a word: "
+
+## @brief Text shown when the word holds a character that is not a letter.
+INVALID_INPUT_TEXT: str = "Sorry, only the letters A to Z are allowed. Try again."
+
+## @brief Text shown before the code words are printed.
+RESULT_TEXT: str = "Phonetic code words:"
+
+## @brief Text encoding of the data file.
+DATA_ENCODING: str = "utf-8"
+
+## @brief Exit status of a session that ended normally.
+EXIT_OK: int = 0