Substitutions with regex

[kiith-sa]

Allow the user to specify substitutions to change certain words/strings.

Match by regexps.

E.g. "Component": Component

(This is a trivial example; more useful would be e.g a regexp matching all different cases and synonyms of word Component starting/ending with word boundaries)

These substitutions should be processed before both DDoc and Markdown, so they may contain both DDoc macros and Markdown syntax.