srp.js: add a bunch of type-checking assertions
params: store as sets of bignums, add 'hash' and 'N_length_bits'
tests: switch to parameter sets instead of separate N/g/hash-alg arguments
srp.js: convert API to accept parameter sets
srp.js: improve assertIsBignum()
Merge pull request #19 from warner/parameter-sets

change API to accept "parameter set" instead of discrete N/g/hash-alg values