Meta issue for technical upgrades in 2.0+

[ctb]

This is a meta issue for technical upgrades/enhancements to khmer in the 2.0+ series. Please discuss additions to this list in the comments; item-specific thoughts go in the item-specific issues. (There is some overlap with the items in #1216, user experience.)

Note: please don't put awesome new science upgrades here. That goes elsewhere :).

1. Dynamic scaling of core data structures. Tracked and discussed in Dynamic scaling of core data structures #1215.
2. Enable new hash functions, including k > 32 and single-stranded hashing. Tracked in Enable multiple hash functions #27.
3. Allow more flexible counting - binsizes other than 1 and 8 bits, minifloat, etc. Tracked in Add other binsizes into hashtable than 1 bit and 8 bits. #51.
4. Clean up graph traversal API and enable more powerful & flexible graph traversal. Tracked in Graph traversal upgrades #1229.
5. Load/save GFA. Maybe? being tracked in write counting or presence table to disk in GFA format #726.