SeedingData: enforce de Bruijn graph property for path storage

This patch enforces the de Bruijn graph property. The new path
storage subsystem will refuse to store paths that break the de
Bruijn property.

Resolves-bug: https://github.com/sebhtml/ray/issues/142
Resolves-bug: https://github.com/sebhtml/ray/issues/141
Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
SeedingData: use the GraphPath storage code to compute seeds

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
SeedingData: refactor code so that m_content is abstracted

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
SeedingData: use 2-bit encoding for paths

Resolves-bug: https://github.com/sebhtml/ray/issues/144
Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
SeedingData: plugin options are parsed by plugins

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
use constants for symbols

Signed-off-by: Sébastien Boisvert <sebastien.boisvert.3@ulaval.ca>
Merge branch 'master' of https://github.com/sebhtml/ray