Add a khmer.load function

[luizirber]

Right now we have two functions:

• khmer.load_countgraph
• khmer.load_nodegraph

It should be possible to figure out which one is the right one (based on the file headers?) and have one function khmer.load that calls the appropriate function for each data structure.

[standage]

Relevant thread: kevlar-dev/kevlar#67.

For now, it should(?) be easy enough to add new ht_types for *table data structures. But just as we're modularizing storage, hash functions, etc, we should consider adding a new field indicating which hash function was used. This would require a major version bump though, so not until we're ready for 3.0.