Clean up some man pages

[Rangi42]

Fixes #1497

• gbz80(7):
  • Breaks the instructions down into more categories
  • Puts the simplest category, load instructions, first
  • SWAP belongs with the shift/rotate instructions, not with BIT/RES/SET just because they're all prefix-encoded
  • CPL belongs with the bitwise logic instructions (it's bitwise logical NOT)
  • .Bl -tag -width Ds should make the flag effect lists more compact in HTML than .Bl -hang -compact
• rgbasm(5):
  • Renames "Unions" to "Allocating overlapping spaces in RAM" to match the other subsection headings
  • Reorganizes the "Defining data" subsections to have ROM ones first and then RAM ones
  • "Requesting alignment" belongs with the "Defining data" subsections
• rgbds(5):
  • The "RPN expressions" subsection heading was all-caps like a top-level section heading

[ISSOtm]

Thank you! This seems like indeed a very useful and welcome improvement. I merely happened to notice a single possible wording improvement while skimming; beyond it, consider this as an approving review—if you agree with the suggestion, feel free to merge this PR right after applying it :)

Resolved