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Use native :numref: macro instead of numsec extension
Trivial: Add SPDX tags to source files
chapter2: fix reference to chapter6
Add 'handheld' chassis type
Fixing some typos and adding missing dots, commas, and hyphens
Add version to specification text
Add Devicetree logo to html and pdf output
Add an SVG logo
Update Arm copyright years thru 2021
