Update licensing information

Dependencies

• [2] HP7KRXCE Add REUSE-compliant licensing information
• [*] NG5QXPZH Extract Account into separate crate
• [*] YDK6X6PP add a library of important types for beancount
• [*] 754VVGV6 Prepare crate for release

Change contents

• edit in beancount/account/tests/basic.rs at line 2
  [2.53]

  [2.53]
  + // SPDX-FileCopyrightText: 2024 Markus Haug (Korrat)
• edit in beancount/account/src/lib.rs at line 4
  [2.149]

  [2.149]
  + // SPDX-FileCopyrightText: 2024 Markus Haug (Korrat)
• edit in beancount/account/README.md at line 3
  [2.245]

  [2.245]
  + SPDX-FileCopyrightText: 2024 Markus Haug (Korrat)
• edit in beancount/account/Cargo.toml at line 2
  [2.338]

  [2.338]
  + # SPDX-FileCopyrightText: 2024 Markus Haug (Korrat)