A simple metadata parser can be useful in markdown documents.
This commit introduces the feature, with the following syntax:
--- or ««« at tstart of the document,
(optionally) followed by a alphanumeric format identifier
followed by key value pairs separated by a colon and a space
followed by --- or ÂÂÂ
Also, adds methods for retrieving the parsed metadata, namely:
getMetadata() and getMetadataFormat
Closes#260
