Bring peg-multimarkdown submodule up to date
Replace Config with RbConfig in Rakefile
Reflect the fact that {parsing,utility}_functions.c have been split into h and c files
Update tests submodule

The latest version (August 2014) of the test suite doesn’t pass,
because development of peg-multimarkdown stopped in early 2013. This
change takes a version of the tests from April 2013, which seem to pass
ok.