add debug symbols by default

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
store a path as a sequence instead of a vector of vertices for efficiency

Resolves-bug: https://github.com/sebhtml/ray/issues/138
Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>