Add conjugate links during GFA I/O #116

Job	Run time
🚧 Build SPAdes	1m 49s
Nextera L.monocytogenes	5m 23s
IonTorrent E.coli K12	31m 22s
Contigs E.coli JGI lane 7	3m 50s
Full run M.ruber JGI lane 9	5m 49s
Mate-pairs B.faecium	2m 6s
Multicell B.cereus TruSeq 100x	4m 21s
Single-cell P.heparinus JGI lane 7	2m 36s
metaSPAdes JGI 150	15m 51s
metaviralSPAdes ERR525599	15m 17s
PacBio M.ruber	3m 43s
plasmidSPAdes C.callunae	7m 7s
Saves E.coli 100K	5m 8s
Saves E.coli UCSD lane 1	8m 41s
Single reads E.coli Deeptrench	1m 38s
	1h 54m 41s

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