Parsing switch in braced parameter

[magicant]

• Define syntax
• Define errors that may happen while parsing
• Implement parser
• Use parser
• Ensure corner cases are tested (e.g. ${#-?}, ${#:-})
• Support context-dependent results (text v. word)
  • Tilde expansion
  • Single- and double-quotes
  • Allow escaping }
• Implement FromStr
• Refactor

---

unit	word	${x-word}	"text"	"${x-text}"
Tilde	Special	Special	Literal	Literal
Single quotes	Special	Special	Literal	Literal
Double quotes	Special	Special	Special	Special
\\	Special	Special	Special	Special
\"	Special	Special	Special	Special
\}	Special	Special	Literal	Special
\{	Special	Special	Literal	Literal

[magicant]

Support context-dependent results (text v. word)

This part seems going to be rather complicated, so I work on it in a separate PR.