Editorial updates for LAS 1.5

[esilvia]

What is the issue about?

No response

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
• "Code" formatting isn't working as expected.
• Add ISO link for calculating epoch? WKT for LAS 1.5 #144 (comment)
• Update ASPRS logo: https://github.com/ASPRSorg/LAS/blob/master/source/_static/asprslogo45.png
• Scrub lingering references to geotiff
• Remove references to PDRF 4 and 5 in WDP VLR

[esilvia]

@hobu You mentioned being able to replicate the Sphinx styling in the RTD builds. I've been playing around with it off and on for a few days and I still can't figure it out. The issue is primarily with the table formatting -- I don't care so much about it matching LAS 1.4 so much as I care about the tables being as readable as possible, and the borders & shading in particular stand out to me as glitchy. Any chance you can take a crack at it?

Edit: Here's a PDF from a recent LAS 1.5 build to show you what I mean. Pay particular attention to Table 3 (header block), Table 7 (PDRF 6 definition), and Table 8 (bit field encoding) as noteworthy examples using different styling techniques.

LAS.pdf