Enable Substitutable Text

[reid-spencer]

Textual content in riddl such as doc blocks or quoted strings needs to allow parameterized substitutions. It is proposed that RIDDL support:

• Config files that simply contain name:value pairs where names define substitutable names in strings and values are the substituted value: name: value
• Substitutions occur using a ${name} syntax in a string: domain foo {???} briefly "Has a ${name} substitution from the yaml file" would yield a briefly of "Has a value substitution from the config file"
• Substitutions can have parameters like: domain foo {???} briefly "Has a ${name:p="value"} so that if the yaml file contained: name: "substitution for p: $p" then the resulting briefly would be: "Has a substitution for p: value"