digraphs: minor shiar proposals updates

digraphs: minor shiar proposals updates

Mostly some subtle composition key reassignments:
- Capitalize letters in !X clicks (easier to type).
- eS for capital esh, because the S is the significant (phonetical)
  component.
- Add sl for long S, which seems like a good mnemonic, and similar to
  other long-legged proposals.
- mL analogous to rL (probably better to use alternatives to Xp if there
  are any).
- K/ for kip sign, since stroked letters are always composed with slash,
  while dash usually means a macron or bar above.