Editorial updates for LAS 1.5

[esilvia]

What is the issue about?

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Issue description

Editorial changes not to forget before the final release:

• LAS 1.4 as the latest version is explicitly referenced multiple times throughout the specification, especially in the header block and introductory sections.
• Ensure that LAS 1.5 is the new reference point.
• Collapse LAS 1.4 revision summary
• Convert Intensity normalization to formatted math equation
• Prettify tables
• Standardize around numbers as numerals (esp. Return Number section)
• Cross-link all references to Global Encoding (esp. Return Number) using RST semi-automated substitution links