Remove direct Sundown dependency
Parser refactor orgin

The aim of this major refactor is to bring easy syntax extensibility
via parser modularity. See https://gist.github.com/zdne/55b7a38f52ca642e123b
the parser prototype.

This commit / refactor also introduces new redesigned Markdown parser – https://github.com/apiaryio/markdown-parser.
Reporting & section context parser data origin

Parsing foreign asset blocks.
Code block signature check origin. Additional asset tests.
Excessive indentation check origin
WIP: Header parser refactor in progress
Completed HeadersParser refactor
Finish HeadersParser refactored tests
WIP: PayloadParser refactor in progress
PayloadParser fixes done
PayloadParser tests are refactored
Add symbol reference support to PayloadParser
Started on ParameterParser
WIP: ParameterParser refactor almost done
Finished ValuesParser
Refactored ParameterParser tests
Don't modify blueprint.h
ParametersParser refactor
Optimized parser code
Finished default for processUnexpectedNode